LISBON, Portugal -- The United States and the four former Soviet republics with nuclear arms signed an agreement yesterday that opens the way for ratification of a 1991 treaty to drastically reduce the number of long-range weapons stockpiled during the Cold War.
Three of the newly independent republics -- Ukraine, Belarus, and Kazakhstan -- also agreed to destroy or turn over all strategic nuclear warheads to the fourth republic, Russia, and to adhere "in the shortest possible time" to the 1968 Non-Proliferation Treaty.
The result of yesterday's agreement leaves the United States with the prospect of having to deal by the end of the century with only one nuclear power in what was formerly the Soviet Union.
While many uncertainties remain, the signing also marks a major step toward dispelling fears that nuclear arms could be used as political weapons, if not purely military ones, as the former Soviet republics jockey with one another for influence.
The four new nations were the only four of the 15 former Soviet republics where long-range nuclear weapons were deployed. All four agreed yesterday to adhere to the Strategic Arms Reduction Treaty, commonly known as START, which was signed by Presidents Bush and Mikhail S. Gorbachev last July after nine years of U.S.-Soviet negotiations.
Five months later, the Soviet Union ceased to exist.
The agreement, which in effect converts the U.S.-Soviet treaty into an international document, was signed after the opening earlier yesterday of a 62-nation conference on aid to the former Soviet republics.
"We have laid the foundations for further stabilizing reductions in strategic offensive arms and expanded the nuclear non-proliferation regime," Secretary of State James A. Baker III said.
The agreement "significantly lowers the risk of nuclear war," the secretary added.
Also yesterday, the Associated Press reported that the United States unveiled a $20 million plan to reduce the risk of nuclear reactor accidents in Russia and Ukraine and invited other nations attending the aid conference to join. Mr. Baker also announced a U.S. proposal to develop food markets in the new nations and to assist them in converting war plants to civilian pursuits.
The arms reduction treaty must now be ratified by all five tTC national legislatures. Mr. Baker said that the administration would be asking Congress to begin the ratification process as soon as possible. Administration officials hope the process can be completed during the current session of Congress.
But substantial areas of uncertainty remain concerning the former Soviet republics.
A statement in Russian released by Foreign Minister Andrei Kozyrev after the signing indicated that it was Moscow's preference that START not be put into action until Ukraine, Belarus, and Kazakhstan turn over or destroy all warheads on their territory. The three other republics have expressed concern throughout the process of turning over all nuclear weapons to Russia.
In a letter to Mr. Bush released yesterday, Ukraine and Belarus called for international supervision of the disarmament process.
Administration officials said after the signing that the four republics "are still working out their basic relations among themselves and not having a very easy time of it."
Six months of talks leading to agreement on this protocol were apparently fraught with clashes of sensitivities among the four nations, which must now negotiate complex questions of how the missiles will be removed from Belarus, Ukraine, and Kazakhstan, who will supervise the process and how it will be verified.
Ukraine now ranks as the third-most-powerful nuclear nation in the world; Kazakhstan is fourth.
Signing the arms document were Mr. Baker, Mr. Kozyrev of Russia, Foreign Ministers Anatoly Zlenko of Ukraine and Petr Kravchenko of Belarus, and Kazakhstan's State Counselor Tulegen Zhukeyev.
After ratification of START, signers of the treaty would begin to reduce long-range nuclear warheads on missiles and on bombers in three stages over seven years.
All short-range, or tactical, nuclear weapons have already been returned to Russia by other republics in which they were deployed. Russia is pledged to destroy them.
At the time of the signing of START, the United States had about 11,600 strategic nuclear warheads, divided among ballistic missiles, cruise missiles and bombs. Under the treaty, that number would be reduced to about 8,600 warheads by the end of the century.
The former Soviet Union would have reduced its nuclear warhead arsenal from the current level of about 10,222 to about 6,500.
The United States had originally hoped to sign agreements reaffirming the treaty with only Russia, but the other nuclear nations of the former Soviet Union insisted on joining the talks.