The United States, reacting briskly to Soviet threats to begin moving new nuclear weapons into eastern Europe, accused Moscow yesterday of "unwarranted threats of retaliation" against U.S. plans to upgrade NATO forces with Pershing II and cruise missiles in December.

The State Department said in a statement that the Soviet warning, made on the eve of the economic summit of western leaders, "is tantamount to a demand for effective military superiority and thus global hegemony."

The U.S. response marked the latest round in the escalating war of words over missile deployment in Europe.

Last Thursday, President Reagan said a go-ahead on deployment of the medium-range Pershings and U.S. cruise missiles is necessary to push the Soviets into serious negotiations on nuclear weaponry.

In Brussels yesterday, a NATO spokesman warned that the new Soviet threats would put a chill on European-theater arms control talks. "They the threats do not contribute to a favorable political climate," the spokesman said.

But U.S. and NATO officials also said they saw the latest Soviet statement, which threatened further deployment of European-targeted SS20 missiles and introduction of nuclear weapons into Warsaw Pact countries, as an overt attempt to influence summit talks that began yesterday in Williamsburg.

The summit is designed to bring together the leaders of seven major industrial nations for personal talks on the world's economy. But there have been hints that the European missile controversy will be discussed by Reagan and West German Chancellor Helmut Kohl.

Although the Bonn government officially denied Friday that Kohl would broach the issue with Reagan, the recently elected West German leader is known to be eager to take some sort of U.S. compromise proposal to Moscow in July for his first meeting with Soviet leader Yuri V. Andropov.

The United States plans to begin deployment of 572 medium-range Pershing II and cruise missiles in December in response to what the State Department called a "massive nuclear buildup" against western Europe by the Soviets.

Most of the U.S.-Soviet propaganda war centers on British and French nuclear weapons independent of those of NATO forces. The Soviet Union contends that such weapons, including 162 land-based missiles, must be counted in attempts at mutual reduction of nuclear weaponry during arms reduction talks in Geneva.

In its latest volley, the State Department again rejected that argument.

"The British and French systems are nationally based strategic deterrents designed to defend France and Britain, not to deter attacks on the other countries of NATO," a State Department spokesman said.

No Soviet ally possesses nuclear warheads, and the Soviets have been reluctant to move nuclear warheads and launchers into their satellite countries because of political instability in eastern Europe.

The State Department also rebuffed the Soviet warning about lifting a self-imposed "moratorium" on deployment of mobile SS20 missiles, contending that "SS20 deployments continued uninterrupted last year" despite the "alleged" moratorium. The Soviet Union denies that charge.

The State Department also criticized the Soviets for failing to deal with global limits on SS20s and other intermediate-range missiles "despite the fact that many SS20s stationed in Asia can reach parts of Europe, and all could be rapidly deployed against Europe."