Mikhail Gorbachev announced Friday the Soviet Union is halting production of weapons-grade uranium and will shut down two more nuclear reactors that produce plutonium for nuclear weapons by the end of next year.

In a remarkably brief address in London's Guildhall, the Soviet president called his unilateral action "another major step toward the complete cessation of production of fissionable materials for use in weapons."Gorbachev reiterated promises he made at the United Nations in December that the Soviet Union would soon begin paring 500,000 men from its standing army and withdrawing troops and tanks from Europe and the Chinese frontier.

Gorbachev made a strong appeal for world disarmament, but he warned the process could falter if the West did not reciprocate.

After the address, broadcast live throughout Britain and the United States, Gorbachev and his wife, Raisa, called on Queen Elizabeth II at Windsor Castle.

Speaking at Guildhall, the city's seat of government for 1,000 years, Gorbachev said the world has reached a crossroad in which it has to choose between peaceful interdependency and "a policy of force rooted in the past.

"If NATO goes ahead with its program of modernizing tactical nuclear weapons," he said, "this is bound also to devalue much of what has been achieved under the INF treaty" on medium-range nuclear weapons that he signed with President Reagan in 1987.

Gorbachev said in addition to the 1987 shutdown of an industrial reactor for the production of weapons-grade plutonium, "we are planning to shut down two other such reactors this (year) and next without commissioning new units to replace them.

"We have completed the construction of a facility for the destruction of chemical weapons and indeed to invite soon your representatives to visit it," Gorbachev said.

Reiterating earlier promises, the Soviet leader said armed manpower would be cut by 12 percent, the military budget by 14 percent and weapons production by nearly 20 percent.

Military factories are being switched to production of consumer goods, and military transport planes would be redeployed to carry civilian cargoes, he said.

He said the new Supreme Soviet, a legislative body to be selected by the recently elected parliament, will publish the nation's defense budget, most of which is now concealed. But he said the ruble's non-convertibility makes comparison with Western military expenditures difficult and "we are looking for the most appropriate way of presenting our data."

The speech got a standing ovation from the civic and political leaders at Guildhall and a ringing endorsement by Prime Minister Margaret Thatcher.

Having sat before him listening to the speech, she called him "one of those rare people who has the vision, the boldness and the sheer power of personality to change the whole future of his country and to have a profound effect on the wider world as well."

"We want you to succeed in your task," she said. "We're ready to help in practical ways."

On Thursday, Gorbachev complained to Thatcher that the Bush administration's review of U.S. foreign policy was delaying important talks on nuclear arms reductions.

Gorbachev told Thatcher that the 21/2-month-old U.S. foreign policy review threatens the momentum of the talks, Soviet Foreign Ministry spokesman Gennady I. Gerasimov told reporters after the leaders met for four hours Thursday.

President Bush ordered the review after he took office in January. U.S.-Soviet talks on reducing long-range nuclear weapons have been postponed indefinitely.

"We understand that the new administration needs time to study foreign policy because there are new faces there and some of them don't know what foreign policy is about," Gerasimov said.

But he said Gorbachev told Thatcher the Soviets "don't want this pause to become an interval which will lead to losing momentum in this process of disarmament."

At a banquet she gave in his honor at 10 Downing St. Thursday night, Thatcher told Gorbachev she could not accept his proposal for eliminating all nuclear weapons by the year 2000.

He replied that she considers him a romantic but that his vision "reflects the hard realities of our time."