Soviet leader Mikhail Gorbachev has sent Libyan leader Muammar Qaddafi a message reaffirming Moscow's commitment to Libya's defense, the official news service Tass reported today.

Gorbachev's message, sent yesterday according to the news agency, said the Soviet Union "firmly intends further to fulfill its commitments in terms of further strengthening Libya's defense capacity."

"This, as we see it, is of special importance for your country in the present situation," Gorbachev concluded, underscoring the Kremlin's apparent intent to continue its arms-supplying relationship with Libya, one of its closest and most strategically placed allies.

Gorbachev's letter followed the announcement yesterday that Moscow was calling off next month's meeting between Foreign Minister Eduard Shevardnadze and U.S. Secretary of State George P. Shultz.

Today, Foreign Ministry spokesman Vladimir Lomeiko said Washington was to blame for the cancellation of the May meeting, but he indicated that yesterday's announcement does not rule out a meeting at a later date.

Even though Moscow sought to make Washington pay a price for the Libyan raid, some diplomats here said it was not a costly one and speculated that it may have left Soviet allies feeling uneasy.

Today, at the press briefing, Lomeiko dodged a question from an African reporter on what Soviet allies could expect from Moscow if they are attacked by the United States. He ruled out any Soviet military response, saying, "Any use of force is counterproductive."

Most diplomats here see the Soviet response to the latest Libyan crisis as being largely defined by Soviet-Libyan relations which, while close, are often uneasy.

At the briefing, Lomeiko gave a summary of Gorbachev's letter, but would not define what Moscow's commitments to Libya specifically entailed.

The letter comes after a visit to Libya last week by a high-level Soviet delegation, headed by K.F. Katushev, head of the Soviet Council on Foreign Economic Relations who is known to have dealt in the past with arms supplies.

No details are known about the trip by Katushev, who left Tripoli one day before the American attack. The timing of his visit, after the March 25 confrontation between Libyan and U.S. forces in the Gulf of Sidra, indicated that he had come to at least affirm, if not increase, Soviet arms shipments, western diplomats here said.

Libya is one of the world's biggest buyers of Soviet arms, with purchases estimated at more than $20 billion in 1983. Since 1984 Libya has been using oil to pay its arms debts, estimated by one source at between $4 billion and $5 billion. Western diplomats here said the Soviets have been defensive about the level of their response to the March 25 clashes. At the time, the Soviets offered full rhetorical and moral support to Libya, but made it clear they wanted to avoid any further involvement.

In his message to Qaddafi, Gorbachev listed actions taken by the Soviets in reaction to the raid, including registering protests with both the United States and Britain.

The British ambassador in Moscow, Bryan Cartledge, was summoned to the Foreign Ministry this afternoon where, according to Tass, he was told by Anatoly Kovalyov, a deputy foreign minister, that Britain was an accomplice in the U.S. attack.

Although Libya is one of Moscow's best customers and allies in the Arab world, the two countries have not signed a friendship and cooperation treaty, the standard pact linking Moscow and its close allies. Among Arab nations, Syria, Iraq, South Yemen and North Yemen have friendship treaties with the Soviet Union.

Diplomats here attributed the lack of a treaty to Moscow's reluctance to embrace Libya too closely as long as Qaddafi is its leader. His unpredictability, his hostile relations with his neighbors and his special brand of revolutionary politics, mixing terrorism and Islam have made Moscow nervous, diplomats say.

In 1983, during a visit here by Libya's second-in-command, Abdul Salaam Jalloud, both sides declared an intention to negotiate a treaty. But last October, when Qaddafi came here on a state visit, no treaty was signed. At the time, Libya indicated that it was the unwilling partner, but many diplomats here have concluded that the hesitation was largely on Moscow's side.

There have been other signs of Moscow's displeasure with Qaddafi's erratic ways. His delivery of Moscow-supplied ground-to-ground missiles to Iran apparently irritated the Kremlin, and, according to diplomatic sources, Qaddafi was informed of Moscow's displeasure during his October visit.

Moscow is a major arms supplier for Iraq, now in the sixth year of a war against Iran.

According to one western diplomat, Libya's deliveries to Iran apparently ceased shortly after the October visit although they may have resumed since.

Moscow, which anchors its Middle East policies around its closest ally in the region, Syria, has recently tried to broaden its diplomatic reach in the region, establishing diplomatic relations with the Persian Gulf states of Kuwait, Oman and the United Arab Emirates.

In the view of Arab diplomats here, too close a relationship with Qaddafi has been seen as a liability with other Arab states which are also uneasy about some of his policies.