LONDON, DEC. 8 -- West European governments hailed today's signing of the U.S.-Soviet nuclear missile treaty as antinuclear activists popped champagne corks and a Sicilian mayor exulted that it "takes death off our backs."

Some Europeans, however, expressed qualms.

Several French commentators charged that the superpowers have stripped America's allies of a major defense by agreeing to eliminate intermediate-range, land-based missiles from the continent.

Antinuclear activists drank champagne toasts outside the Soviet and U.S. embassies in London as President Reagan and Soviet leader Mikhail Gorbachev signed the treaty in Washington. The bottles were marked "Summit '87 Vintage."

"Just for a day, it's 'Champagne for Nuclear Disarmament'," said Alec Howe, spokesman for Britain's Campaign for Nuclear Disarmament.

Hundreds of Italians gathered in the main square of Comiso, a town in Sicily where U.S. cruise missiles are deployed, to cheer as an official presented U.S. and Soviet diplomats with silver plaques bearing peace symbols.

"It is good, not only for us, because it takes death off our backs, but because it is good for all humanity," said Rosario La Perna, the town's mayor.

The signing of the treaty led European newscasts. Several national networks, including the British Broadcasting Corp., extended regular evening news programs to broadcast the ceremony live.

British Prime Minister Margaret Thatcher, who conferred yesterday with Gorbachev during a refueling stop for his jetliner at an English air base, told reporters, "It's a marvelous Christmas present, an extra piece of good will and a lovely way to end the year."

But earlier today, shouting above opposition jeers in the House of Commons, she refused to promise she would not replace the land-based missiles banned under the treaty with U.S. nuclear missiles fired from submarines or warplanes.

"With regard to all our other defenses, we have a positive duty to see they are modernized and effective," the Conservative prime minister told Neil Kinnock, the Labor Party leader.

Kinnock said Britain would wreck the treaty if it permits deployment of new U.S. missiles "either by innovation or some so-called process of modernization."

Polish leader Gen. Wojciech Jaruzelski sent messages to Gorbachev and Reagan saying that "what even recently seemed impossible has now become reality." He added, "The first significant step has been made on the road leading to a world free of nuclear arms."

Prime Minister Gro Harlem Brundtland of Norway also sent letters to the superpower leaders. She wrote that the treaty "can also trigger progress in other arms control negotiations, especially those concerning reduction of strategic weapons, strengthen the conventional stability and the banning of chemical weapons."

American cruise and Pershing II missiles deployed in Britain, Italy, West Germany and Belgium and Soviet medium-range missiles targeted at Western Europe are to be removed over three years. The countdown starts if and when the U.S. Senate ratifies the treaty.

France and Britain, Western Europe's only nuclear powers, will retain and modernize their own arsenals, mainly sea-launched long-range missiles.

The 12-nation Economic Community issued a statement over the weekend praising the accord.

Chancellor Helmut Kohl told West German citizens they should be pleased with the treaty.