The United States responded today to Soviet charges that it is unfit to play host to the United Nations with the warning that if the Soviets and others want to move the organization's headquarters out of New York, "we will put no impediment in your way."

In fact, added U.S. representative Charles Lichenstein, "The members of the U.S. Mission to the U.N. will be down at dockside waving you a fond farewell as you sail into the sunset."

A U.S. mission spokesman modified the stand later by noting that Lichenstein's remarks were made in response to a Soviet "provocation" and were not intended "as any new departure in U.S. policy."

The American preference has been and remains that the U.N. headquarters stay in New York, officials said.

Lichenstein's scathing rejoinder came at a meeting of the U.N. committee dealing with diplomats' problems in New York, after the Soviet representative charged U.S. authorities with failing to protect Soviet delegates and with making it impossible for Soviet Foreign Minister Andrei Gromyko to attend the General Assembly session that opens here Tuesday.

The Soviet diplomat, Igor Yakovlev, questioned why the "U.N. headquarters continues to be located in a country which fails to fulfill its obligations" as host.

Lichenstein called the Soviet charges "palpable falsehoods."

He said there was no threat to the safety of Soviet diplomats here, and made the case that the American offer to let Gromyko's plane land at McGuire Air Force Base in New Jersey rather than Kennedy or Newark airports was an "eminently reasonable" alternative that offered "no impediment" to his U.N. trip.

In a bitter reference to the Soviet destruction of a Korean jetliner on Sept. 1, Lichenstein added: "We will not shoot Gromyko's plane down even if it should inadvertently stray from its flight path."

Then, turning to the Soviet charge that the United States had violated its obligations as U.N. host under the 1947 Headquarters Agreement, Lichenstein said:

"If in the judicious determination of the members of the U.N., they feel they are not welcome and they are not being treated with the hostly consideration that is their due, then the U.S. strongly encourages such member states seriously to consider removing themselves and this organization from the soil of the United States. We will put no impediment in your way."

Few delegates at the meeting took the U.S. threat seriously, but there was a general feeling among both Western and Third World representatives that the United States had made a tactical mistake and played into Moscow's hands by giving Gromyko an excuse to cancel his U.N. visit.

"The American action let Gromyko off the hook," said one Asian diplomat friendly to the West. "He would have felt the heat here, and would have been told in all his bilateral meetings with other foreign ministers that Soviet behavior toward the Korean plane was unacceptable."