Back when the most recent bull market was young, many traders believed the time had finally come for true 24-hour, around-the-globe U.S.-style stock trading.

Several new companies sprung up to provide the trading services, creating a potential threat to the Nasdaq Stock Market and its counterparts. The new companies petitioned federal regulators for rule changes that would give them a chance to compete, and, by and large, the Securities and Exchange Commission granted their requests in the name of providing competition.

One of the first casualties of the market bust was the dream of robust 24-hour trading, which many experts now believe won't happen for years, if ever. That has left several firms and exchanges scrambling to capture as much trading business here in the United States as they can, raising concern among regulators that a central tenet of the nation's market system -- that all investors are treated fairly -- may get lost in the turmoil.

With that backdrop, the SEC is scheduled to begin a series of hearings today to examine whether the upheaval is creating unnecessary risks for investors.

The SEC is not specifically examining the operation of 24-hour global trading markets in these hearings. But the agency will be exploring the underlying efficiencies and rules that are needed to make such a global market system work.

Among other things it will examine is what kind of data that retail and institutional investors require, who should pay for that data, and what kind of mechanism is needed to link markets to make sure investors get the best execution of their trades.

It will also try to determine whether self-regulatory organizations, such as the New York Stock Exchange and NASD, are doing enough to protect investors, whether their functions should be reallocated, and whether there are risks in allowing such organizations to become for-profit companies.

The agency is expecting testimony today and on Nov. 12 from some of the biggest players on Wall Street, including officials of Nasdaq, the NYSE, regional stock exchanges, electronic trading networks, and groups representing institutional and retail investors as the SEC tries to shape the role of future markets.

Nasdaq championed the idea of a 24-hour global trading system and made it the center of its business strategy. It envisioned a series of exchanges, linked by an international network, open to ordinary investors day and night.

Nasdaq, figuring it would raise millions going public like the Internet companies that listed on it, sank millions of dollars into creating Nasdaq operations in Japan and Europe.

The effort to plaster its silicon-encrusted name on stock markets around the world, however, has stumbled. Nasdaq recently announced it was pulling out of its Nasdaq Japan venture with Softbank Corp., despite spending $20.1 million on the effort.

Nasdaq also scaled down its aspirations in Europe, to focus solely on Germany, in a partnership with the Bremen and Berlin stock exchanges. Still, given the recent failure of Neuer Markt in Germany, which modeled itself after Nasdaq, even this modest effort is being met with skepticism.

"I'm highly skeptical of an exchange going into another country that expects to do it better than the people who are already there," said Sang Lee, an analyst at Celent Communications, a research firm in Boston.

But John Hilley, chairman and chief executive of Nasdaq International, said Nasdaq has not abandoned its vision and asserted that Europe could play a decisive role in the emergence of a 24-hour global stock trading system.

Hilley said that there are still factors that argue for a 24-hour global stock-trading network. The high costs of cross-border trades in Europe should make a Nasdaq system attractive, he said. A typical cross-border trade in Europe costs five times as much as one within a domestic market, according to a study last year by Celent.

Critical to its success, said Hilley, will be Nasdaq's ability to attract German retail investors.

Another key issue is whether European investors are content to trade U.S. stocks during U.S. market hours. If they are clamoring for such trades outside normal U.S. trading hours, that demand can be the basis of a 16-hour trading system, said Hilley.

Similarly, if Asian investors show an interest in buying and selling U.S. and European shares when those markets are closed, all of the constituencies necessary to make a genuinely nonstop global trading system viable will be on board.

Nasdaq began drawing up blueprints for a system spanning the globe because of the explosion in the number of retail investors during the bull market who spent their dinner hour pumping money into the after-hours trading market. But now those investors have fled the after-hours market in droves, leaving mainly institutional investors.

Brooks McFeely, the president and chief executive of MidnightTrader, a news service for after-hours traders, refers to this phenomenon as the "shaking out of the dumb money."

"I'm not trading hardly at all right now," said Richard Walstra, a former active trader and an accounting professor at Dominican University in River Forest, Ill. He will return to the market when it recovers, he said, but with "more patience, because I found I probably overtraded."