NEW YORK » Banks pouring money into technology funds, wealthy clients and institutions clamoring to get pieces of startups, expectations of stock market debuts building as Wall Street’s machinery kicks into second gear, some investors with memories of the Internet bust a decade earlier are wondering whether this sudden burst of activity spells danger for the industry once again.

With all this exuberance, valuations are soaring. Investments in Facebook and Zynga have more than quintupled the implied worth of each company in the last two years. The social shopping site Groupon is said to be considering an initial public offering that would value the company at $25 billion. Less than a year ago, the company was valued at $1.4 billion.

"I worry that investors think every social company will be as good as Facebook," said Roger McNamee, a managing director of Elevation Partners and an investor in Facebook, who co-founded the multibillion-dollar private equity fund Silver Lake Partners at the height of the boom. "You have an attractive set of companies right now, but it would be surprising if the next wave of social companies had as much impact as the first."

Funds set up by Goldman and JPMorgan Chase have invested in Internet startups like Facebook and Twitter or in funds with stakes in those startups. Even the mutual fund giants Fidelity Investments and T. Rowe Price have stepped up their efforts, placing large bets on companies like Groupon and Zynga.

Thomas Weisel, founder of an investment bank called the Thomas Weisel Partners Group that prospered in the first Internet boom, says he is "astounded" by the amount of money now flooding the markets.

"I think it’s much greater today," he said. "The pools of capital that are looking at these Internet companies are far greater today than what you had in 2000."

Yet there are notable differences between the turn-of-the-century dot-com boom and now. For one,B the stock market is not glutted with offerings. In 1999, there were 308 technology IPOs, making up about half of that year’s offerings, according to data from Morgan Stanley. In 2010, there were just 20 technology IPOs, based on Thomson Reuters data.

More important, the tech startups that have attracted so much interest from investors have real businesses not just eyeballs and clicks. Companies like Facebook have fast-growing revenue. Groupon, which has been profitable since June 2009, is on track to take in billions in revenue this year. And since 1999, when 248 million people were online (less than 5 percent of the world’s population), broadband Internet and personal computing have become mainstream. About one in three people are online, or roughly 2 billion users, according to data from Internet World Stats, a website that compiles such numbers.

"In those days, you had tiny, little companies going public that hardly had a business plan," Stefan Nagel, associate finance professor at Stanford University, said. "And now you’re talking about only a few companies companies that are already global and with revenue."

With such a small, elite group, the potential fallout if things go badly would be limited, some investorsB say.B "Yes, we have a frenzy again," said Lise Buyer, a principal of the Class V Group, an advisory firm for companies considering initial public offerings. "But the frenzy is on a very select group of companies. Facebook is clearly Secretariat, but there are a few other championship horses they are looking to bet on."

For Wall Street, the initial attraction to Internet startups in the 1990s was the opportunity to earn fees from taking the companies to market. At its peak in 1999, the industry made $1.3 billion in underwriting fees, according to data from Thomson Reuters.

But as enthusiasm surged, many firms also rushed to make investments for their clients and themselves through special-purpose funds and direct investments. And in many cases the banks got burned just as ordinary investors did.

"The investment pools that we did back in 2000 did extremely poorly, because many of those companies went from filing an IPO to bankruptcy courts in a matter of months," said Weisel, whose firm was acquired by Stifel Financial last year.

In 1998, Goldman Sachs Capital Partners, the bank’s private equity arm, began a new, $2.8 billion fund largely geared toward Internet stocks. Before that fund, the group had made fewer than three dozen investments in the technology and communications sectors from 1992 to mid-1998, according to Goldman Sachs documents about the fund.

But between 1999 and 2000, the new fund made 56 technology-related investments, of about $27 million on average. In aggregate, the fund made $1.7 billion in technology investments and lost about 40 percent of that after the bubble burst. (The group, which manages the money of pensions, sovereign wealth funds and other prominent clients, declined the opportunity to invest in Facebook early this year.)

Philip A. Cooper, who in 1999 was head of a separate Goldman Sachs group that managed fund of funds and other investments, recalled that investors were clamoring, "We want more tech, we want more."

Bowing to pressure, he created a $900 million technology-centric fund in 1999, and within eight weeks he had nearly $2 billion in orders. Despite the frenzy, he kept the cap at $900 million.

"There was a lot of demand, but we couldn’t see any way we could prudently put that much capital to work," said Cooper, who has since left Goldman.

Other Wall Street firms, including JPMorgan Chase and Morgan Stanley, also made a number of small to midsize investments during the period. In 1999, for instance, Morgan Stanley joined Goldman Sachs and others in a $280 million investment in CarsDirect.com, which scrapped its initial plans to go public when the market deteriorated.

"We thought we were going to double our money in just a couple of weeks," said Howard Lindzon, a hedge fund manager of Lindzon Capital Partners and former CarsDirect.com investor. "No one did any due diligence." Lindzon lost more than $200,000 on his investment.

An online grocer, Webvan, was one of the most highly anticipated IPOs of the dot-com era. The business had raised nearly $1 billion in startup capital from institutions like Softbank of Japan, Sequoia Capital and Goldman Sachs. Goldman, its lead underwriter, invested about $100 million.

On its first day, investors cheered as Webvan’s market value soared, rising 65 percent to about $8 billion at the close. Less than two years later, Webvan was bankrupt.

Today, the collective amount of money that Wall Street banks are pumping into Internet startups, on top of the surging cash piles from venture capital groups, hedge funds and private equity, is a major concern for some investors.

Over the last five months, many venture capital players have raised giant chunks of capital. One Facebook investor, Accel Partners, is about to raise $2 billion for investments in China and the United States, while Bessemer Venture Partners is said to be closing in on $1.5 billion for a new fund. Greylock Partners, Sequoia Capital, Andreessen Horowitz and Kleiner Perkins Caufield &

Weisel, who has also been tracking hedge fund activity, finds the numbers dizzying. Countless hedge funds are investing in private placements "dozens and dozens of hedge funds are doing the same thing," he said.

As cash continues to pile up, the fear is that all this money cannot be put to work responsibly. With only a few perceived "winners," some investors must be choosing losers or paying too much, Meeks said.

"When you see the valuations being bandied about I do think, boy, these better be really special companies."