U.S. Trade Representative Carla Hills Wednesday embraced a broader-reaching U.S. antitrust policy aimed at opening foreign markets wider to U.S. exporters.

"I am enthusiastic" about such a policy, which is expected to be announced this week by the Justice Department, she told the House Ways and Means Committee's Trade Subcommittee.The policy, it is speculated, will likely focus on Japan, although Mrs.

Hills said she and Attorney General William Barr "have not talked in terms of a particular country."

Under the policy, the United States presumably could penalize foreign companies for engaging, to the detriment of U.S. exporters, in such activities as group boycotts, market allocation and price fixing in their home markets.

Mrs. Hills stressed, however, that the policy "simply reverts" to an antitrust policy that had been in force in the early 1980s.

She also argued that the Japanese business practice of corporate interlocking directorates, known as keiretsu, is not necessarily illegal. The problem, she said, is whether the practice masks anti-competitive practices.

The United States, she said, seeks more "transparency" in the way Japan does business.

Japanese antitrust law, she noted, is very similar to U.S. law, but the Japanese government's enforcement of it has been questionable.

Mrs. Hills, meanwhile, was cautioned by Rep. Sam Gibbons, D-Fla., the Ways and Means subcommittee chairman, that unless the United States concludes the Uruguay Round trade negotiations this year at the General Agreement on Tariffs and Trade in Geneva "there would be a very, very slim chance that Congress would extend fast track."

The administration says "fast track" - the authority to negotiate the Uruguay Round subject only to a congressional "up or down" vote - is essential to the round's conclusion.

The present fast-track authority runs through mid-1993.

In other comments, Mrs. Hills said it is "very difficult" to predict when the U.S.-Mexican-Canadian free-trade negotiations will be completed. "It is very possible," she said, "that we could conclude an agreement this year, indeed this spring, but we're not there yet."