Mikhail S. Gorbachev looked more at home in the splendor of London's ancient Guildhall than in shirt-sleeves in Cuba during the Soviet president's six-day trip abroad.

Gorbachev's gains, if any, from private talks with Cuban president Fidel Castro in Havana may not be apparent for some time, but he reaped positive news during his later stop in London.

Gorbachev got a ringing endorsement from Britain's staunchly anti-communist prime minister and a promise of a visit from Queen Elizabeth II. The queen would be the first British monarch to visit Russia since the Communists killed Czar Nicholas II and his family, who were cousins of the queen's forebears.

But U.S. officials said they were disappointed that Gorbachev's visit to Cuba produced no signal the Soviets were prepared to disengage from Central America, where the superpowers are pitted against each other by proxy.

Gorbachev and Castro stressed solidarity, though Cuba has shown no inclination toward liberalization policies being adopted in Moscow, Beijing and much of Eastern Europe.

But Gorbachev, who has shown more interest in wooing Western banks and business than in propping up Third World revolutionaries, made no move to ease Cuba's huge debt burden. Analysts had speculated some measure of debt forgiveness might be forthcoming as a goodwill gesture during the Soviet President's first visit to Cuba.

Instead, Gorbachev said the Cuban government should be more careful in spending Soviet aid.

"As in the past, the Soviet Union and Cuba have a common approach to the key problems of international affairs," Gorbachev told the Cuban National Assembly. "We are resolutely against any theories and doctrines justifying the export of revolution or counterrevolution and all forms of interference in the affairs of sovereign nations."

White House spokesman Marlin Fitzwater said he welcomed the statement but said it was not supported by action. The Bush administration, which just committed to end military aid to the Contra rebels in Soviet-backed Nicaragua, had hoped for a clearer signal that the Soviet government would reduce arms shipments to the Sandinista regime, he said.

But seasoned observers in Havana said even if that was Gorbachev's intention, he would not have said so in Cuba, Nicaragua's strongest ally.

Soviet Foreign Ministry spokesman Gennady I. Gerasimov said people have come to expect too much from the Soviet leader.

"It's the rabbit-from-the-hat approach," Gerasimov said. "With other politicians, you don't expect so much, but when Gorbachev speaks, you expect him to pull out a rabbit every time."

But after leaving the island, a Gorbachev aide hinted that the Soviet Communist Party chief may try to mediate the long-running feud between Cuba and the United States.

Although Castro's public remarks were peppered with anti-American slogans, Georgi Shakhnazarov, a foreign policy adviser to Gorbachev, said the Cuban leader indicated privately he wants to normalize relations with the United States.

Asked if Gorbachev could bring the two neighbors back together, Shakhnazarov said, "The general secretary tries not to miss any opportunity" to encourage better relations.

In London, the Soviet leader addressed magnificantly robed British luminaries in Guildhall. He then received from Prime Minister Margaret Thatcher the endorsement he has sought from the West since launching his modernization campaign four years ago.

Speaking at Guildhall, Gorbachev summarized his goals for an international television audience.

"We are building an open, democratic and free society which has learned the lessons of its past, a society based on law and responsibility, a society that keeps its citizens well informed," Gorbachev said. "We are building a society that rests on its citizens' initiative and enterprise, on Soviet socialist patriotism and dedication to human socialism aimed at elevating the human being."

Thatcher 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 told Gorbachev. "First because we believe that in your vision lies a better life for the Soviet people, but also because every step toward greater democracy, human rights and freedom of choice in your country brings us closer together."

And she pledged: "We're ready to help in practical ways, too, where our help is sought and desired."