The companies announced Monday that America Online Inc. the top Internet service provider, will buy Time Warner Inc, the world's largest media company, in a stock transaction.

Experts said the takeover will likely not cause serious antitrust problems. "It does not appear there are antitrust issues that would provide a significant impediment to this transaction," said Steven Salop, a professor of antitrust law at Georgetown University Law School.

Antitrust lawyer Marc Schildkraut, of Howrey & Simon in Washington, agreed that the merger would probably pass muster after a close examination.

"They will be looking at the same kinds of things they looked at when Time Warner acquired CNN," Schildkraut said.

That merger — announced in 1995 and approved in 1997 — raised questions about vertical integration. The Federal Trade Commission was concerned that the new company could raise the prices for programming because it would both produce programmes and distribute them through the country's second largest cable system.

In this merger, AOL would be in a position to distribute content produced by what is now Time Warner.

At this point, the Justice Department and Federal Trade Commission have yet to sort out which agency will be reviewing the transaction.

Whichever agency does handle it will hear from certain consumer groups, which do not like the deal.

The consumer groups are concerned about the possibly interlocking ties between AOL, Time Warner and No. 1 cable operator and long distance giant AT&T; Corp.. Time Warner is the No. 2 cable operator.

AT&T; is seeking to acquire Media One Group Inc., which owns 25 percent of a joint venture called Time Warner Entertainment which holds the bulk of Time Warner's assets, including over 11 million cable television subscribers. Time Warner owns the remaining 75 percent of the venture.

If AT&T;'s deal is approved and AOL and Time Warner merge, AT&T; would own 25 percent of a venture that holds a substantial portion of AOL Time Warner's cable assets.

Time Warner and Media One also jointly own a high-speed Internet access service called Road Runner. AT&T; owns the largest stake in the only other major cable ISP, Excite AtHome Corp..

Consumer groups also fear that the interest of AOL, which has more than 21 million subscribers who dial up on telephones to get on the Web, will suddenly change because it would suddenly have a behemoth cable company of its own to sell high-speed Internet access.

Until now, AOL has been fighting to gain access to high-speed Internet access systems provided through cable. Cable companies have insisted that they have the sole right to provide Internet service to their customers and can exclude AOL.

"AOL has been the hammer for opening up the broadband networks and this would change that," said James Love, who heads the Consumer Project on Technology in Washington. He said that AOL has had the resources to engage in "hand-to-hand combat" at city councils to require access.

"Right now they're the outsider trying to get in. With the merger, they're the insider," Love said.

But Howard Morse, a former Federal Trade Commission official now with the Washington law firm of Drinker, Biddle & Reath, expressed doubt that such views would cut muster with the antitrust agencies.

"I think it's one thing to talk about market power," Morse said. "It's a different thing to talk about political power."

Antitrust agencies examine whether mergers may give one company too much power in the marketplace. If the agencies find that a combined company would gain the power to significantly raise prices in a marketplace, they reject the merger.