A U.S. negotiating team headed toward Moscow yesterday on a new phase in the continuing search for a strategic arms limitation treaty between the superpowers.

State Department spokesman Hodding Carter said the mission, headed by Director PauL C. Warnke of the Arms Control and Disarmament Agency, was "agreed to in principle" during Geneva meetings in July between Secretary of State Cyrus R. Vance and Soviet Foreign Minister Andrei Gromyko.

Informed officials said the Warnke team, which includes representatives of the State and Defense departments and the Joint Chiefs of Staff, will deliver a response to positions set forth by Gromyko on several issues unresolved during the Geneva meetings. The team hopes to obtain Soviet reactions to the U.S. ideas, as the basis for further Washington decision-making before a Gromyko trip to the United States.

The present expectation is that Gromyko will come to Washington for meetings with Vance and perhaps President Carter in mid-September, prior to New York sessions with Vance a week or so later during the early days of the United Nations General Assembly session.

Administration officials continue to express confidence that a SALT II treaty can be successfully negotiated late this year or early next year, at the latest. Even after the Vance-Gromyko talks this month, however, high-level decisions and probably a summit meeting between Carter and Soviet President Leonid I. Brezhnev will be necessary to settle all the outstanding issues, sources said.