A new nuclear strategic arms accord with the Soviet Union is virtually beyond reach before the current pact runs out on Oct. 3, some administration sources acknowledged privately yesterday.

Secretary of State Cyrus R. Vance and Soviet Foreign Minister Andrei A. Gromyko will not meet again, before September, State Department spokesman John H. Trattner said.

Vance and Gromyko "will meet twice in the general time frame of September," the spokesman said, and one of the meetings will be at the annual U.N. General Assembly meeting in New York. The site of the other meeting was not dsoclosed, although Trattner said "SALT will be discussed at both of the meetings." He said he could not discuss the impact of this timing on the Oct. 3 expiration date.

It is standard procedure for Gromyko and the Secretary of State to meet twice in the autumn, one at the United Nations and once in Washington, sometimes at the White House.

President Carter, however, has been emphasizing that there will be "at least" two Vance-Gromyko meetings before the accord runs out, as evidence that the negotiations are making progress in Geneva and in other discussions.

Carter last month spoke of two Vance-Gromyko meetings before mid-September. In his press conference Monday, the President dropped that time reference and said Vance and Gromyko "will meet at least twice more between now and the expiration date for the present agreement." This indicated, the President said, that discussions are "moving in the right direction."

Administration officials were anxious late yesterday to dispel any impression that the absence of a Vance-Gromyko meeting before September means that new obstacles have developed in the SALT talks or U.S.-Soviet detente, or that the administration is slowing down its timetable.Officially, they also declined to concede that a new SALT accord is ruled out before Oct. 3.

One administration officials said the September dates now set for the Vance-Gromyko meetings are simply the result of the pressure on Vance's schedule, which includes "a trip in July to the Middle East" and "another in August to China."

But apart from scheduling problems, the administration has been anxious to avoid being portrayed as "rushing into a new agreement" with the Soviet Union by Oct. 3 that would expose it to political attack for undue readiness to compromise in the nuclear negotiations.

For domestic political reasons alone, numerous sources have said, it would be more advantageous for the administration to have an agreement after Oct. 3 rather than before. Some senior planners privately doubt that a new U.S.-Soviet accord will be reached this year.

President Carter repeatedly has told members of COngress he does not feel "bound by any deadline."

The current five-year limitation on American and Soviet intercontinental strategic nuclear weapons came into force on Oct. 3, 1972. Vance said on May 4 that if no renewal is ready by the expiration date, "we can either extend the agreement, if the Soviets are willing to do so, or we continue as if there were a continuing agreement."

Vance said, "I don't feel that we are fighting any deadline that is going to cause us to take actions that are not wise or prudent."