The United States, led by President Reagan, belittled the Soviet Union's announcement of a Euromissiles moratorium yesterday, but U.S. officials responded in low-key fashion to a Soviet threat to retaliate against U.S. deployment plans.

Reagan, who had been tipped off a day in advance about the Soviet announcement, told a joint session of the Oklahoma legislature that "a freeze simply isn't good enough because it doesn't go far enough." Reagan made a similar statement Monday before the Tennessee legislature during his two-day stumping tour.

In Oklahoma, the president renewed his Nov. 18 appeal for the Soviets to dismantle Europe-based nuclear missiles in return for cancellation of U.S. plans to deploy new Pershing II and ground-launched cruise missiles starting next year. Reagan described this U.S. "zero" proposal as fair, and said, "If President Leonid Brezhnev is serious about real arms control--and I hope he is--he will join in real arms reduction."

A written White House statement issued in the name of spokesman Larry Speakes and oral comments by Secretary of Defense Caspar W. Weinberger, presidential counselor Edwin Meese III and other officials took a harsher tack than Reagan did in his statements.

The written statement said: "The 'unilateral moratorium' offered by President Brezhnev is neither unilateral nor a moratorium." It went on to charge that the proposal seeks to maintain Soviet superiority, divide the West and secure for the Soviets "unchallenged hegemony" over Europe.

The statement also said, as did the president, that by limiting his freeze to missiles in the European part of the Soviet Union, Brezhnev remains free to build up mobile weapons on the other side of the Urals, where they still would threaten most of Western Europe and be in position to move westward rapidly.

Neither Reagan nor most other administration officials addressed Brezhnev's vaguely worded warning that "retaliatory steps" would be taken to place U.S. territory under "analogous" danger if new U.S. missiles are deployed near the Soviets' European border.

A senior State Department official noted at a press briefing on the U.S. reaction that "Cuba is not specifically mentioned" in Brezhnev's warning and said that "we're not sure what Brezhnev is referring to." The official said "threatening noises" were nothing new in Soviet statements about the Euromissiles issue, but he avoided any expression of apprehension or alarm on this score.

Questioned by reporters, the official did say that deployment of intermediate-range nuclear weapons in Cuba would clearly violate the U.S.-Soviet understandings that ended the 1962 Cuban missile crisis. Asked what the U.S. reaction to such a violation would be, the official replied, "I don't think I need to say any more."

Another reporter asked what would happen if such Soviet weapons were to be deployed in Nicaragua. "I think it is fair to say that would be a very serious development," the official said.

Another official, a veteran analyst of Soviet affairs, expressed doubt that Brezhnev's remarks were a threat to place missiles in Cuba. The main Soviet concern, this official said, is the sharply reduced warning time that would result from the placement of modern U.S. missiles near the Soviet borders.

More likely than a land-based response in the Caribbean or Central America, according to this official, would be deployment of submarine-launched cruise missiles and additional submarine-launched ballistic missiles near the United States.

Several officials pointed out earlier Soviet threats to Western Europe in terms similar to those directed against the United States yesterday.

On Oct. 6, 1979, for example, shortly before NATO decided to accept U.S. medium-range missiles on European soil, Brezhnev said that such deployment "would change essentially the strategic situation" in Europe, causing the Soviet Union to take "necessary extra steps" that would aggravate the situation. He specifically warned West Germany that its situation "would considerably worsen" if it accepted the U.S. weapons.

As in the statement yesterday, the emphasis in Brezhnev's October, 1979, speech was conciliatory--in that case, an announcement of a unilateral withdrawal of some Soviet troops and tanks from East Germany and the statement of a readiness to reduce its Euromissiles if the West were to refrain from new deployments.

The principal concern indicated by the statements of U.S. officials yesterday was that Brezhnev's announcement of a moratorium may appeal to public opinion in Western Europe, the political battleground for Soviet-American debate about Euromissiles and many other issues.

Reagan's Nov. 18 address proposing the "zero option" plan for Euromissiles was addressed largely to Western Europe. Some U.S. officials thought several statements by Brezhnev, including that of yesterday, were also aimed largely at swaying this strategic audience.

Reagan and his team had plenty of time to prepare their response. White House officials said the statements by Reagan to the Tennessee legislature Monday, seemingly addressed to a "nuclear freeze" resolution on Capitol Hill, actually had been delivered with the aim of preempting the expected moratorium announcement by Brezhnev.

Reagan's statements Monday were quoted in many news accounts in Europe and elsewhere alongside Brezhnev's Tuesday morning proposal.

Also quoted in a number of accounts was a State Department estimate, made public Monday, that the Soviets recently increased their deployment of SS20 missiles to 300, from an earlier U.S. estimate of 280.

Meese, in the most colloquial response to Brezhnev, compared it to a football game in which one side is ahead 50-to-0 two-thirds of the way through and tries to freeze the score for the rest of the game. He added, "That's not exactly a fair kind of thing or something that would be in the interests of protecting the people of Europe."

Weinberger, at a newspaper convention in San Antonio, Tex., said the moratorium proposal, by leaving some 300 Soviet missiles in place, "essentially leaves the count at about 300 to nothing."

Several congressional Democrats were more positive about Brezhnev's announcement. House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) called the moratorium "a movement in the right direction." Sen. Edward M. Kennedy (D-Mass.), a coauthor of a congressional proposal for a worldwide nuclear freeze, said he disagrees with Brezhnev's proposal because it applies only to European-based systems, but Kennedy said the announcement should be used as an opportunity for "progress on a broader scale."

The two-page written White House statement, handed to reporters immediately after Reagan's address to the Oklahoma legislature, also took issue with Brezhnev's proposal to limit the operations of missile submarines, calling it "not serious." The Soviet proposal, the statement charged, would increase the vulnerability of a key part of the U.S. deterrent force and thus is "entirely self-serving."

The White House statement also condemned the Soviet proposal for a ban on deployment of long-range ground-launched cruise missiles, calling it "another transparent effort" to distrupt NATO plans.

The U.S. statement said principles of equal and verifiable reductions underlying Reagan's Nov. 18 Euromissile proposal would also form the basis for the American position in negotiations about reducing strategic nuclear weapons. The U.S. side postponed starting such negotiations after the imposition of martial law in Poland three months ago.