LONDON, SEPT. 18 -- Governments around the world today hailed the U.S.-Soviet agreement to eliminate medium-range nuclear weapons as a historic breakthrough, and expressed hope that it would lead to other improvements in East-West relations and armaments reductions.

Amid the almost universal approval, however, there were broad differences among U.S. allies over what the next step should be.

Some clearly hope that the accord announced in Washington today will lead quickly to further cuts in nuclear weapons. But others see it as marking a hiatus in the nuclear arms-control process that will give the allies time to digest and plan for its ramifications and to concentrate more closely on other areas of East-West imbalance and tension, including conventional forces.

In Britain, Foreign Secretary Geoffrey Howe said the signing of the agreement, at a summit that President Reagan said he hoped to hold with Soviet leader Mikhail Gorbachev this fall, would be a "profound development" and a "formidable achievement" for the North Atlantic Treaty Organization.

A spokesman for the West German government said Chancellor Helmut Kohl was "deeply satisfied" with the "global elimination, through negotiations, of a whole category of nuclear weapons."

Kohl attributed the success to the "constructive conduct of negotiations by the American president," the solidarity of NATO and his own government's "substantive contribution."

The spokesman said that it was Bonn's agreement to a Soviet demand -- that its 72 Pershing IA missiles, carrying U.S. nuclear warheads, be dismantled -- that had created the "decisive preconditions" for accord.

Reiterating the terms of that decision, he said that "when the American and Soviet intermediate-range nuclear forces are removed in accordance with the treaty, the German systems will also be removed."

In a news conference today in Washington, Secretary of State George P. Shultz said that the process of dismantling all missiles in Europe with a range of between 300 and 3,000 miles -- 332 U.S. cruise and Pershing II missiles and an estimated 683 Soviet missiles, most of which carry three warheads each -- would take three to five years.

Belgium said it would remove the 16 cruise missiles deployed in its territory under a timetable to be established by NATO. Following a Cabinet meeting in Brussels, Prime Minister Wilfried Martens said Belgium would unilaterally scrap plans to deploy 32 more next year if a final accord is signed. "We will not wait for the ratification . . . of this accord to take this decision," Martens said in a local television interview.

In the Netherlands, where the scheduled deployment of cruise missiles in November 1988 long has been a divisive political issue, Foreign Minister Hans van den Broek said he was "particularly relieved now that this agreement is within reach." Although he said it was "premature to make any binding statements" before NATO begins talks on a timetable for removal, van den Broek said "personally, I would wish not to have to deploy."

Neither Britain nor Italy, which are scheduled to add more cruise missiles to those already stationed in their territories, commented on their plans for new deployments.

Britain's Campaign for Nuclear Disarmament, which organized major opposition to the cruise deployments here in 1983, said that the tentative treaty was "a vindication . . . and a tribute to the strength of worldwide antinuclear opinion."

Former British defense secretary Michael Heseltine, who oversaw the arrival of the missiles here, said the accord was a triumph for the West, and vindication for those who "held their nerve in the face of Soviet missile deployment by bringing cruise and Pershing missiles to Europe."

In their statements of approval today, a number of NATO governments signaled their hopes and fears for what would come after the accord is signed on medium-range missiles.

Both Washington and Moscow have indicated that, despite the considerable disagreement remaining between them, they hope to reach an accord to eliminate up to 50 percent of their strategic nuclear systems, the long-range intercontinental ballistic missiles that each has targeted on the other's territory.

West Germany has said that it hopes the next step will be talks aimed at reducing tactical, or battlefield, weapons with ranges of less than 300 miles. The removal of medium-range missiles, leaving West Germany as the primary reachable target for the remaining short-range systems, is a political problem for the Kohl government.

But NATO's military command believes that the removal of medium-range weapons will make it more vital than ever for the short-range weapons to stay in place and be improved.

NATO Secretary General Lord Carrington said here yesterday that NATO's 1983 Montebello decision to enhance its tactical nuclear weapons stocks "must also be carried out if we are to preserve the essential minimum of deterrence."

A senior British official said that his government was particularly concerned that the agreement covering medium-range missiles would lead to pressure from some quarters to pull back from the Montebello agreement. He expressed hope that the allies would react "calmly and slowly" and would stick to the principles agreed by Reagan and British Prime Minister Margaret Thatcher after the abortive Reagan-Gorbachev summit in Reykjavik, Iceland, last October and later approved by all of NATO.

Beyond the question of short-range systems, Britain and France worry that new impetus toward superpower strategic cuts would endanger their own independent strategic nuclear arsenals.

A French spokesman recalled today that Prime Minister Jacques Chirac told the United Nations last year that France would not accept any nuclear freeze involving its own weapons, Reuter reported from Paris. France, he said, also had rejected participation in a nuclear test ban, another subject on which the Americans and Soviets said they had made progress this week.

In other comments, Japan's Prime Minister Yasuhiro Nakasone called the accord "extremely good news" and said he hoped "the talks will steadily advance, leading to an agreement being firmed up."

In Ankara, Reuter reported, NATO-member Turkey, which borders the Soviet Union, said it was pleased by the agreement.