With opposition to NATO enlargement mounting among a vocal minority in the U.S. foreign-policy establishment, the issue has emerged as the most immediate diplomatic challenge for the second Clinton administration. Some critics want President Bill Clinton, freed of the necessity of facing the electorate again, to abandon the NATO initiative or at least fold it into a wider, slower program for European stability.

While discussions in the alliance have been proceeding for more than two years, the debate is gaining visibility in Washington because, according to strategists on both sides of the issue, the administration intends to press Moscow for a broad preliminary deal on European security, including enlargement, in the next few months.

President Boris Yeltsin is due to visit Washington in March or April, but "it will be very hard to have him here before this thing is settled," according to a State Department official.

"You're going to see a lot of activity starting now, especially with Congress," said Deputy Secretary of State Strobe Talbot, a leading and confident-sounding advocate of enlargement.

The administration — and other proponents of enlargement — have deliberately confined the issue to diplomatic channels and avoided domestic discussion, said Robert Zoellick, who served in the Bush administration, because both presidential candidates supported expansion. Mr. Zoellick and Mr. Talbot

said that the administration — and Republicans — plan to press the case for enlargement in time to build momentum before a NATO summit meeting in July.

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