"This is an immensely positive and welcome step," said Deputy Secretary of State Strobe Talbott. "It is a very significant contribution to the security of the region and to the new independent state of Ukraine. It is also important for the national security interests of the United States."

Russia has said it would not put into effect the Strategic Arms Reduction Treaty, which made deep cuts in long-range nuclear weapons, until Ukraine signed the nonproliferation treaty.

Both the Russian Parliament and the United States Congress have also said they were waiting for that to happen before taking up ratification of a subsequent arms accord, known as Start II. Taken together, the two treaties would slash the American and Russian stockpiles by two-thirds, so each country would have between 3,000 and 3,500 warheads.

Both Republicans and Democrats in Congress have generally been favorably disposed toward aid to the Ukraine.

Over the last three years, both the Bush and Clinton Administrations have repeatedly pressed Ukraine to join the nonproliferation treaty, fearing that failure to join would sow discord between Ukraine and Russia. But until today, Ukraine's Parliament had delayed a decision, seeking to use their warheads as a bargaining chip for international respect, foreign aid and security guarantees.