For the New York Stock Exchange and Nasdaq Stock Market, the most visible threat born of technology has been the little start-ups that duplicate what they do for a fraction of the cost.

But even these aspiring electronic exchanges are dwarfed by a much more ominous rival on the other side of the Atlantic.

Representatives of Deutsche Boerse Group, the parent of Germany's biggest stock exchange, have been sweeping through Wall Street, proposing to install terminals that could ultimately link U.S. traders to bidders--and blue-chip stocks--overseas. They have talked to Nasdaq about a joint venture. And they have requested an exemption from Securities and Exchange Commission rules that bar foreign corporations from trading in the United States.

"I am aware that Deutsche Boerse wants to expand in the United States," Richard A. Grasso, chairman of the New York Stock Exchange, said during a recent interview. "I think it's fine if they want to compete, but we want a level playing field to compete there, that's all. Markets in a world of technology should not be limited by boundaries of water."

Plans are very preliminary and regulatory hurdles are high. So it is hard to say what role Deutsche Boerse will ultimately play in the high-stakes race to reshape the way stocks are traded on this side of the Atlantic.

"We are not willing to comment on the U.S. strategy," said a Deutsche Boerse spokesman in Germany. "These are plans we'll make here and announce when the time comes."

But several Wall Street sources said that Deutsche Boerse is aggressively studying a plan to market its technology as a platform to trade stocks, options and futures in the United States.

"They are taking a successful evolution to an electronic model in their own market and thinking about how and when it makes sense to migrate that model to other parts of the world," said a top trader at a major Wall Street firm for whom Deutsche Boerse officials recently provided an elaborate presentation. "It is easy to see how this technology can travel well."

The expedition comes as stock markets around the world, armed with new technology, are attempting to enter one another's turf. The battle is particularly acute in the United States, where the two top stock markets have been criticized for being slow to embrace a more open trading system.

"It's a big land grab now," said Matthew Andreesen, president of the Island, one of several electronic trading networks awaiting SEC permission to become an electronic stock exchange.

The U.S. markets are battling back by installing new technology and fleshing out their own overseas plans. Grasso, after years of guarding the floor brokers who essentially own the Big Board, recently unveiled a plan to build an electronic trading system for small orders that bypasses their "specialists" who otherwise handle all orders in a stock.

The Frankfurt stock market is the fourth-largest in the world, behind New York, Tokyo and London. But Chairman Werner Seifert, a Swedish-born former McKinsey & Co. consultant, has vowed that new technology will help it to become the biggest in the next decade.

In 1997, Deutsche Boerse paid Andersen Consulting $90 million to design an electronic quote-driven system that would phase out much of the work force on the floor. The product was Exchange Electronic Trading--Xetra for short--a graphics-based system that offers traders equal access to a central order book. That is the model that SEC Chairman Arthur Levitt Jr. has urged U.S. markets to adopt, saying the proliferation of electronic trading systems has made it difficult to track orders.

Typically, 70 percent to 75 percent of German blue-chip stocks are traded electronically through Xetra. Of Frankfurt's 1,200 brokers, there were once 300 on the floor at any given time; now there are 100.

Seifert is counting on the system to dissuade German companies from listing their stocks in the United States. If Xetra can display a German company's stock fluctuations to American institutions--something the New York Stock Exchange can offer--it would strip a prime enticement for listing in the United States.

Already, Deutsche Boerse is working with the Chicago Board of Trade to jointly develop an electronic trading platform. It is also in talks, sources said, with the International Securities Exchange, an electronic options exchange that was formed by William Porter, founder of E-Trade Group Inc.

On equities trading floors, Deutsche Boerse has an arrangement with Eurex, the world's biggest derivatives exchange, which it co-owns with the Swiss exchange and is based in Switzerland and Germany. Deutsche Boerse is allowed to install Eurex terminals--and those Eurex terminals in theory can display Xetra information.

Now, Eurex has about 20 screens installed at U.S. institutions, and another 50 are in the pipeline. "They [Deutsche Boerse officials] are trying to flood the market with their screens, so they can go to the U.S. and say, look, all these people have our screens, so now you should let us trade," said a Wall Street executive.

The SEC will not allow Deutsche Boerse to install trading screens for Xetra in the United States, because the stocks that would be traded on those screens are German corporations that do not follow the same accounting and disclosure standards as those in the United States.

But, as one Wall Street source versed on Deutsche Boerse's plans said, "anything else in theory is possible." It could buy an exchange or set up a new exchange, the source said. Or it could provide an exchange with an electronic trading platform.

Both the London and Frankfurt exchanges have had talks with Nasdaq. Deutsche Boerse offered to essentially run a stock pipeline into Germany to connect investors there with the top 350 Nasdaq stocks.

Nasdaq was cut out altogether, though, when Deutsche Boerse made a deal with the London exchange for a pan-European exchange. But they have been unable to agree on ownership and the choice of technology to be used for its trading platform.

Nasdaq has responded with a plan to open in Europe by the first quarter of 2001. But the market is already packed, and many people believe that it may be too late. "What would be Nasdaq's asset except for the brand name?" asked one European trader. "They are not even positioned for a growth market that picks the companies that are really sexy."

CAPTION: Chairman Werner Seifert expects technology to lift Deutsche Boerse.