Google Inc.'s initial public offering took a major step forward as the company notified investors that today may be their last chance to submit, withdraw or change bids in the unusual $3 billion electronic auction for stock in the Internet giant.

Separately, Google disclosed that the Securities and Exchange Commission has launched an investigation into the company's issuance of more than 25 million shares of stock and options to employees and others from the fall of 2001 to this summer. The company previously warned that it may have broken state and federal laws by failing to properly register the shares. A number of states are also reviewing the matter, Google said.

Google could close the auction this afternoon and its shares could begin trading in the stock market under the ticker symbol "GOOG" as early as Wednesday. While the company has suggested a price range of $108 to $135 per share, investors are free to bid any price they wish.

Some institutional investors are betting that they may be successful with bids in the lower half of the suggested range, which would value the entire company in a manner that is similar to that of its nearest competitor, Yahoo Inc. Google could set the opening or "clearing" price for the stock as early as this afternoon, and anyone who bid that amount or higher would be allocated shares at the opening price.

The disclosure yesterday by Google is an apparent sign that investor interest in the company's auction has been strong, despite warnings that the profitable company's growth rate is slowing and does not justify such a high price. At the levels being suggested, Google shares would be sold at roughly 150 times profit per share, a level that is extraordinarily high based on traditional methods of valuation.

Google operates the Internet's most popular search engine, an online service that matches the queries of computer users to the Web pages most likely to contain the answers. The company generates most of its revenue from the sale of ads that run alongside the search results.

Google said it would ask the SEC to give its final approval to the prospectus describing the company and its offering at 4 p.m. today. According to the rules of the auction, that would trigger a series of events, including the possibility that bids from investors could be accepted as early as 5 p.m. today.

"If you have submitted a bid, you should access the current prospectus and carefully reconsider your bid(s)," Google said in a notice sent yesterday by e-mail to investors who registered for the auction. "Bids may be accepted by the underwriters in as little as ONE HOUR after the notice of effectiveness of the registration statement is sent to you. Please note that submitting a bid does not guarantee that you will be allocated shares in the offering, if it is completed."

Google posted the latest news about the auction on its Web site, as well as distributing it via e-mail to investors who registered for the auction. After all the bids are in and the auction has closed, Google executives will consult with their lead financial advisers at Morgan Stanley and Credit Suisse First Boston to set the IPO price.

The auction is devised to yield the highest possible price for the company and for early investors in Google who are also selling stock as part of the 25.7 million-share offering. Google has warned that its stock price could be volatile and fall in the first days of trading.

Google has said it may set the IPO price slightly below the "clearing" price to achieve a broader distribution of stock and offset some of the downward pressure that could occur in the first days of trading. Google has said bidders allocated shares may suffer a "winner's curse," in which they end up being allocated shares in the IPO that drop in price once trading begins.

The auction method being employed by Google is a direct challenge to Wall Street, which typically has controlled the price and distribution of shares in IPOs and earned fees in excess of 6 percent. No other company has ever successfully used an electronic auction to sell as much stock as Google wants to, but Google appears to be on the verge of achieving a breakthrough.

Google engineers have devised the technology being used in the auction, and the company has mandated that individual investors willing to buy as few as five shares have the same chance to end up owning Google stock as deep-pocked institutions that have close relationships with Wall Street. Google also has slashed the fees that the 28 Wall Street brokerage firms participating in the deal get paid.