General Motors Co. files a regulatory notice today announcing its intention to begin publicly selling shares of the reorganized company, marking a first step towards unwinding the U.S. government’s 60.8% stake.

GM says certain current individual shareholders will sell common stock, while the company will issue mandatory convertible junior preferred stock and use the proceeds for general corporate purposes.

The mandatory convertible stock converts to common stock on a specific date, but during its holding period provides the investor with greater compensation usually through dividends. Companies typically issue such securities during unstable capital markets.

GM says market conditions and other factors will affect the amount of securities to be offered. A price range has not been set, and the auto maker does not indicate when shares would go on sale, although it is expected sometime in November.

GM’s notice to conduct an initial public offering comes nearly one week later than anticipated, reportedly delayed by a surprise retirement announcement Aug. 12 from current Chairman and CEO Ed Whitacre as the auto maker sorted out a succession plan for the document.

Board member Dan Akerson, who like Whitacre is a former telecommunications executive but also served as a managing director at The Carlyle Group investment firm, will take the CEO’s chair Sept. 1. The 61-year-old will add the chairman’s role by the end of the year.

It was understood Whitacre, 68, would not stay at GM long-term, after President Obama coaxed him out of retirement in July to lead GM out of bankruptcy. He became CEO less than six months later, when the board soured on longtime-executive Fritz Henderson and asked for his resignation.

With the much-anticipated filing finally official, GM embarks on what could be the richest IPO in U.S. history and one of corporate America’s all-time comebacks.

Some experts estimated a stock offering from the Detroit auto maker, newly unshackled from years of cash-slurping debt service and rich labor contracts, to fetch upwards of $20 billion. But media reports today put the figure closer to $15 billion

Two years ago, Visa Inc. raised $17.9 billion in the biggest U.S. IPO to date. The global IPO record was set in July when the Agricultural Bank of China went public in a $19.2 billion deal on the Hong Kong and Shanghai stock exchanges.

But the U.S. Treasury invested some $50 billion worth of taxpayer funds into GM’s bankruptcy and restructuring, so it will take several years of follow-on offerings before the auto maker completely washes off its “Government Motors” label.

In the first round, the government is expected to shed 20% of its investment to bring its ownership beneath 50%.

The auto maker, founded 102 years ago next month, has shown renewed financial strength in its first calendar year back from bankruptcy. Through June and in a miserable sales market in the U.S. and Europe, GM earned some $2.2 billion and its second-quarter profit of $1.3 billion was its best in six years.

But some experts have questioned GM’s decision to go public again after emerging from Chapter 11 protection just over a year ago, saying the company needs to post a lengthier financial track record and capital markets remain shaky.

Kathleen Smith, chairman of Greenwich, CT-based, Renaissance Capital, tells Ward’s otherwise. “It’s not about what you’ve done in the past, it’s about what you’re going to do in the future,” she says.

While GM’s International Operations continue to hum along on the strength of continued growth in emerging markets such as China and Brazil, the auto maker’s long-term viability remains clouded by U.S. sales below 12 million units on an annualized basis and a reorganization of its European unit costing billions of dollars.

GM reveals in the prospectus filed today with Securities and Exchange Commission plans to broaden its North American portfolio by launching 19 new vehicles between 2010 and 2012, focusing on cars and cross/utility vehicles. An additional 27 vehicles are expected between 2013 and 2014.

GMIO will launch 77 new vehicles through 2012 by “leveraging our global architectures, pursuing local and regional solutions to meet specific market requirements and expanding our joint-venture partner-collaboration opportunities.”

In Europe, it will refresh 80% of all Opel/Vauxhall products by the start of 2012 so no model’s styling is less than three years old. Three product launches are scheduled for 2010 and another four in 2011.

Investors likely will express concern over GM leadership, which with Akerson receives its third CEO since Rick Wagoner was ousted in March 2009. Akerson has little auto industry experience, joining GM’s board last year in a shakeup meant to bring in fresh thinking.

GM’s next-highest ranking CEO candidate, Vice Chairman and CFO Chris Liddell lacks experience, as well, although his financial management acumen goes unquestioned.

GM admits in the filing its senior leadership lacks automotive experience and lists that as a potential risk.

“It is important to our success that the new members of the executive management team quickly understand the automotive industry and that our senior officers quickly adapt and excel in their new senior management roles,” GM says.

“If they are unable to do so, and as a result are unable to provide effective guidance and leadership, our business and financial results could be materially adversely affected.”

GM also faces tightening fuel-economy regulations and needs cash to make capital investment in technology to meet those new standards.

“We anticipate that the number and extent of these regulations, and the related costs and changes to our product lineup, will increase significantly in the future,” the auto maker says.

“These government regulatory requirements could significantly affect our plans for global product development and may result in substantial costs, including civil penalties. They may also result in limits on the types of vehicles we sell and where we sell them, which can affect revenue.”

Competition shows no signs of weakening, either, as upstart Korea-based Hyundai Motor Co. Ltd. America continues to win market share in the U.S. and European behemoth Volkswagen AG opens a new plant in Tennessee later this year.

“The global automotive industry is highly competitive, and overall manufacturing capacity in the industry exceeds demand,” GM says.

“In addition, manufacturers in lower-cost countries such as China and India have emerged as competitors in key emerging markets and announced their intention of exporting their products to established markets as a bargain alternative to entry-level automobiles.

“These actions have had, and are expected to continue to have, a significant negative impact on our vehicle pricing, market share and operating results and present a significant risk to our ability to enhance our revenue per vehicle.”

However, Wall Street’s appetite for IPOs appears to be growing. According to Renaissance Capital, 86 companies have gone public this year, up 310% from last year.

Prior to its bankruptcy last year – the biggest in U.S. history – GM spent nearly its entire corporate history as a publicly traded security, and its stock joined the Dow Jones Industrial Index in 1915.

GM was a continuous member of the 30-company Dow index for 84 years, a run second only to General Electric Co., until trading of its shares were suspended on June 1, 2009, ahead of its Chapter 11 filing.

GM says in its prospectus it intends to rejoin the New York Stock Exchange and also list itself on the Toronto Stock Exchange.