Imagine: You need to renew your license plates and suddenly you discover you can't just go to your corner gas station to have your car's tailpipe tested for that all-important certificate giving your car its tailpipe exhaust a clean bill of health.

Nope, you have to drive across town to a new state-run centralized facility to have several sophisticated tests performed that analyze not only tailpipe emissions, but also minute amounts of gasoline vapors leaking out of the fuel system. After waiting in line for more than an hour, you are informed that your 7-year-old vehicle flunked the test and will have to have its emissions control system repaired.

So you make an appointment to have your car fixed at the dealership (it's the only shop in town that has the expensive diagnostic equipment required to do the work) and spend $250 or more and lose your car for a day getting it fixed.

Then you drive across town again, wait in line for an hour, and are informed your car still can't pass the test. Later, your spouse goes through the same hassle with her 3-year-old car.

Believe it or not, this Kafkaesque nightmare -- known to insiders as "ping-ponging" -- already is happening in the U.S. It started in Maine last year and is being phased in by at least four more states in 1995.

By 1998, areas in 28 states that have been designated by the EPA as having pollution levels exceeding federal limits could be affected -- although consumer outrage and the new Republican Congress may force major changes.

Ward's Engine and Vehicle Technology Update newsletter reports that a recent study by General Motors Corp.'s Service Technology Group indicates that 1 million year-old, 3 million five-year-old and 5 million seven-year-old vehicles will fail the test. Average cost of repairs is predicted to be $250 to over $300.

It's all mandated by provisions of the Clean Air Act Amendments of 1990 enacted during the Bush Administration. Developed by the Environmental Protection Agency and called "enhanced inspection and maintenance (I/M 240) vehicle emissions testing," the program is designed to target and fix high-pollution vehicles using laboratory style equipment such as sophisticated gas analyzers and dynamometers, and stringent testing procedures that match more closely the EPA's own in-house laboratory tests -- all housed in a tightly controlled, centralized facility.

I/M 240 also includes using high-tech infrared roadside mobile sensing units that detect high-emitting vehicles as they drive by. The units record the license plate number and then send a ticket in the mail, ordering the owner to have the vehicle tested and fixed if it is caught twice in the same year.

There's no getting around it: Even if some legislation moderates, emissions-control technology will dominate the automotive electronics scene for at least the next five years.

In a recent survey conducted by Ward's Auto World and Siemens Automotive, more than 60% of respondents say engine and drivetrain components will make up between 40% and 49% of the total North American automotive electronics market. For 2000, that range is picked by 41 % of survey participants.

Related electronics also are expected to skyrocket. The market for new diagnostic machines for auto shops doing I/M 240-related maintenance repairs could hit $1 billion, says SPX Corp., a major supplier of such equipment.

It's all being driven by Clean Air Act mandates. Besides I/M 240, all new vehicles also must meet On-board Diagnostics Series II (OBD II) emission rules by 1996, driving one spike. Another level of emissions regulation is expected in 1998, and yet another in 2003.

OBD II is an incredibly complex electronic diagnostic system that monitors no less than 17 different engine and emissions-systems operations. "It's designed to monitor all systems that could have an effect on emissions. We're moving toward a system that will predict how a vehicle will do on an emissions test," says Doug Berens, manager of emission compliance at Ford Motor Co. "Basically we're putting a whole engineering laboratory into the electronics system of car."

Despite the strong desire for cleaner air, a growing number of critics say legislation is pushing current technology -- and the general public's patience -- too far.

The potential cost and inconvenience I/M 240 testing poses to consumers has created such a firestorm of controversy in the U.S. that almost all affected states are negotiating with the EPA to revamp the programs and de-emphasize centralized testing.

Maine has temporarily suspended its program, and Texas, Maryland and Colorado are phasing in only watered-down versions of the test, so far. Arizona is the only state currently conducting full I/M 240 testing, says Ronald J. Ortiz, president of SPX's Automotive Diagnostics Div. and an expert on the new testing program.

Furthermore, automakers are complaining quietly behind the scenes that because of the way the tests currently are calibrated they could erroneously fail thousands -- perhaps even millions -- of vehicles.

Automakers also are worried that some aspects of the test procedures actually could damage emission-control system hoses and tubing in older cars, producing an even greater repair bill for consumers.

Another concern is that the equipment in the centralized testing facilities is so expensive and sophisticated (costing a minimum of $140,000) that repair shops won't be able to afford repair equipment that is precise enough to properly diagnose and remedy the problems the testing facility detects. And even if those repair shops can do the work effectively, critics warn that repairs will cost far more than the EPA now estimates.

A story in the New Hampshire Union Leader -- another state unhappy with I/M 240 -- warns that two hours of repair shop diagnosis time alone can cost $120 or more; replacement of an oxygen sensor $165; and a new catalytic converter, $300 to $900.

Those are indications of what could be in store for owners of cars that fail their new test. "Tuneups won't solve most problems," the story says.

These costs really could hurt low-income owners of poorly maintained used cars. The Illinois EPA has tried to head off this type of publicity by distributing a pamphlet on the I/M 240 program that estimates the average repair bill will be about $150 for cars that fail the test.

But repair shop owners and technicians say that figure is much too low. A key reason is the current system of grading repair-shop performance on the basis of how many repaired cars pass the re-test.

One shop owner says: "There is no way I'm going to sell less than the maximum (needed repair) if it means that I could get my reputation trashed by a contracted state test station."

During the full I/M 240 test -- which takes at least 10 to 15 minutes -- tailpipe emissions are measured on a 240-second dynamometer run, and pressure and purge tests are done on the entire fuel system to ensure there is no gasoline vapor leakage.

Dave Millerick, Ford's manager of emissions planning, says automakers are worried about two main aspects of the test: how they are calibrated and potential damage from pressure and purge tests.

If the extremely precise testing instruments don't allow enough room for normal variances, they could produce high numbers of false failures, which are impossible to fix and only antagonize already irate consumers by ping-ponging them, he says.

Furthermore, he says the pressure and purge tests require technicians to actually cut open tubes and hoses, attach them to the testing equipment, and then repair and reassemble the vehicle's evaporative emission-control systems.

Older vehicles with tubing that has undoubtedly grown brittle could easily be damaged by this procedure, Mr. Millerick warns.

Amazingly, industry sources say the EPA did not consult with automakers about how to implement I/M 240 test procedures prior to creating them.

Nevertheless, automaker officials don't want to publicly criticize OBD II or I/M 240 regulations too much. Like Mom and apple pie, nobody wants to say anything bad about clean air.