Once upon a time, a door was just a door. Pickups had two, minivans had three with a hatch in the back. Cars had two or four. You got in. You got out. What was there to quibble about?

Now a simple door is referred to as a "family entry system." Doors represent different lifestyles, and marketing concepts. Most importantly, they've come to represent life and death in the light-truck marketplace. Not since the great cupholder wars of the late '80s and early '90s has there been such a fuss over such a basic feature.

Sales of Ford Motor Co.'s Windstar minivan have plummeted in part because it lacks a fourth-door option, for instance. And despite tremendous sales momentum and growing production capacity, Chrysler Corp.'s extended-cab Ram pickup may not be able to catch Chevy during the next couple of years because it has no third-door option, analysts say. A Ram pickup with four doors is expected in '98, however. That may do the trick. Unless of course, Chevy comes out with a five- or six-door pickup (just kidding).

Meanwhile, a fourth, driver's side sliding door on General Motors Corp.'s new-generation Venture, Trans Sport and Silhouette minivans is expected to jump-start the vehicles in the marketplace and finally give GM a strong position in that segment - probably at the expense of Ford.

Also, Honda Motor Corp.'s four-door minivan, the Odyssey, is doing surprisingly well, despite sharp criticism by the automotive press for being overpriced, underpowered and not roomy enough. Guess why. Upcoming minivans from Toyota and other Japanese auto-makers also are expected to have a fourth-door option when they are introduced.

Like cupholders before them, the more doors on a truck nowadays, the better.

Even though the fourth door costs $600 extra on most of Chrysler's minivans (it's standard on pricey Town & Country models), 85% to 90% of buyers opt for the feature. That's higher than Chrysler's most optimistic forecast, which was about 75%, says spokesman Rick Deneau. The order rate is 80% for dual-sliders on Pontiac Trans Sport, but they only come as part of a package option on long-wheelbase versions. Starting price: about $24,000. Order rates for Chevy and Olds versions are similar.

The remote control electric sliding minivan door - another example of door mania - is yet again a popular option. Currently a GM exclusive, it costs $400 and is ordered on about 70% of the vans where it is available. Chrysler has been studying power-operated doors for years, but a source says it's unlikely it will add one "unless we can find a better system". Meow.

Besides that, there are extra wide "super doors" (Ford) and "super plug" door innards (GM vans). Suppliers such as UT Automotive are creating new interior door panel designs with built-in cupholders and special storage compartments for items such as purses or umbrellas.

Another supplier, GM's Delphi Interior & Lighting Systems, has even looked at putting a refrigerated cupholder in the door armrest.

And of course, there are arguments over which side is best for a third door on a pickup, and disputes over who invented what door design, and when.

Like the old tale of the lone lawyer going broke until another lawyer moved into town, nobody had much to say about doors until an "extra" one suddenly appeared last year on the driver's side of Chrysler's new minivans. A few months later third doors appeared on extended cab versions of GM and Ford Motor Co. full-size pickups. The trend has been further extended now to compact pickups at GM, and will be followed by Ford next model year with its Ranger - and most likely everyone else.

"People are thinking much more about functionality than they used to," says Lincoln Merrihew, an analyst with DRI/ McGraw-Hill's Global Automotive Group. "Once you get used to a certain functionality, whether it's coffee makers with a clock, or more functions on your VCR, you don't want to give it up."

Adding doors to extended-cab pickups (which have rear seats) is a real no-brainer, Mr. Merrihew says, explaining that the conventional 2-door arrangement that customers have bought without question for years "is like driving a sedan with a trunk that doesn't open."

Even so, before vehicles started to appear with the extra doors, most market research suggested the auto buying public was not clamoring for them.

For instance, a minivan buyer profile analysis done in 1995 by R.L. Polk & Co. (long before the new Chrysler vans debuted) showed that only about 30% of minivan buyers considered an added driver's side passenger door "desirable." Almost half said they weren't at all interested in such a feature. Research done earlier was even less convincing.

Chrysler mulled the addition of a driver's side sliding door for at least five years, says Gloria E. Lara, an executive at UT Automotive who worked for Chrysler in the late 1980s and was involved with the minivan product planning group. The automaker kept balking because market research at the time showed little interest among consumers for another door, but she and other women began pushing for one because they saw the possibilities. "I was carrying around my infant baby at the time, and I said: 'You know what I'm tired of putting in and taking that child seat out. I wish I could do it from the driver's side,'" she recalls.

Other factors slowed the extra doors as well. Adding openings to a vehicle's body structure raises numerous crash-energy management and noise/vibration/harshness (NVH) issues that have to be addressed. The problem is especially acute in pickups lacking B-pillars to provide structural support in side impacts; the doors themselves have to be built to withstand the jolt.

Then there is the added cost of the doors themselves: Instead of a few square feet of plain sheet metal, a door is a very complicated part, explains Kenneth L. Zurek, chief product engineer for modular door systems, at Delphi Interior & Lighting Systems. There are complex hinges and seals involved, plus dozens of mechanical parts such as latches, buttons and window-lift mechanisms - all of which can have a major impact on customer satisfaction and affect warranty costs.

These factors, coupled with apparently lukewarm interest from consumers, reportedly caused Ford to exclude dual sliding doors from Windstar, which was introduced as a '94 model. General Motors Corp. had no plans to offer a four-door option, either, but it lucked out. It had to design a body structure that would allow for doors on both sides of its van because it was building right-hand drive versions for export. Offering doors on both sides as an option then turned out to be a simple matter.

Unfortunately Ford had no right-hand drive plans for the Windstar, and was stuck with a body design that couldn't easily be altered: the vehicle's air/heat and fuel-line hardware are located in the panel behind the driver's door.

Ford's answer to the problem - at least for the next year or two - is a standard extra-wide driver's-side "super door" which will come on "freshened" Windstars due in early '97. Combined with a driver's seat designed to tip up and slide forward, passengers will have easy access to the vehicle interior from the driver's side. But nobody at Ford likes the term "super door." Instead, the big door/sliding seat combination more likely will be referred to as a "family entry system," insiders say.

Competitors call the Ford door a Band-Aid, and say it will be so long that it actually will be difficult to open in a crowded parking lot. Knowledgeable Ford sources sky that isn't so. "It's 2 ins. (5 cm) shorter than the door on a Chrysler Neon coupe," says one, adding that a specially designed door hinge prevents it from being accidentally opened too wide and hitting other cars.

The. door war is even nastier among pickups. Late last year Thomas D. Baughman, chief program engineer on Ford's popular F-Series trucks, accused GM of infringing on Ford's third-door design patents. He argued that Ford developed the concept of a 3-door extended cab and applied for a patent that was issued in 1989.

A GM spokesman denied the claims and said Ford was just mad that Chevy beat Ford to the marketplace. He said GM has used a similar door on its full-size G-vans since the 1960, and that it developed the third door for its extended-cab pickup in a special 23-month crash program.

After a bit of saber rattling on both sides, the controversy has either died down or been settled quietly behind closed doors. Neither side is interested in talking much about the issue anymore. "There was a bit of bravado going on about that, but if all the automakers sued each other, I don't think anyone would be in business. That is not going anywhere," says a Ford spokeswoman.

The third doors in both automakers, vehicles are similar except for seat belt and handle placement.

Whatever the case, the battle is another example of how competitive the market is becoming in full-size pickups. Ford and Chevy always have fought bitterly for sales leadership in big pickups because they are the highest-volume vehicles built in the U.S., and the market so far has hardly been touched by foreign competition. But as more and more consumers buy the big pickups for personal use, rather than for work trucks, they are ordering lots of expensive options - from extended cabs to leather seats - that are making this fast-growing market even more lucrative. For instance, Ford says only 30% of its full-size pickups are used strictly for work

But now Chrysler is becoming a serious competitor, with its dramatically styled Dodge Ram pickups flying off dealer lots and Chevy's aging C/K pickups losing sales momentum. Chrysler reportedly is planning to boost its limited production capacity and make a serious run at pushing Chevy out of the No.2 spot. However, Mr. Merrihew, the DRI/McGraw Hill analyst - and lots of GM insiders - say it won't happen because Dodge can't offer an extended-cab with extra doors until 1998.

The controversy now is slipping down-market into compact pickups. So far, GM is the only automaker with a third door option, but Ford is expected to offer a Ranger with a third door next model year.

Some analysts, however, think Ford goofed by placing the extra door on the same side as its big pickups. Unlike full-size pickups, where passenger-side access is considered preferable, many analysts argue that compact pickups are mainly personal-use vehicles driven by single drivers who want access to the back seat from the driver's side.

All this interest in doors certainly hasn't been lost on suppliers, who are working overtime developing new concepts that will help cut costs and please consumers.

In addition to Gm's power sliding door, Mr. Zurek says Delphi Interior & Lighting Systems has developed a "Super Plug" interior door module that consolidates dozens of components into one part and fits easily into the door assembly. The module reduces costs and improves quality. The new door module debuts on the new GM minivans, and will appear on another '97 vehicle that makes its entrance later in the year.

However, Delphi doesn't want to stop at modular innards, Mr. Zurek says. It also is looking at developing entire door assemblies and then delivering them - completely assembled - directly to the assembly line.

On the consumer side, suppliers such as Delphi and UT Automotive are looking at new ways to pamper drivers and passengers with special pockets to hold purses, cups, umbrellas and other features built into the door panels - which might even be interchangeable, to suit specific needs.

The most extravagant feature Mr. Zurek admits to investigating is a refrigerated cupholder for the door. However, he says the cost of such a device could make it unfeasible.