In what could be a sign that Moscow still intends to abide by the U.S.-U.S.S.R. strategic arms limitation treaty (SALT II), the Soviets yesterday gave advance warning to the United States of new missile flight tests, informed sources said.

Notification of such tests, which are supposed to take place today, is called for in a provision of the SALT II agreement, signed in Vienna last June by President Carter and Soviet President Leonid I. Brezhnev but never approved by the Senate because of a worsening of U.S.-Soviet relations.

In January, in the aftermath of the Soviet invasion of Afghanistan, Carter asked the Senate to postpone work on the new treaty indefinitely, a request that basically acknowledged that the pact had no chance anyway for approval on Capitol Hill in the current national mood.

Yet the administration has consistently said it intends to continue abiding by the terms of the Salt II pact as long as Moscow does. The Soviets, however, have made no similar public statement.

And, at a joint meeting in Geneva last month, the Soviet delegates also declined to discuss various provisions for implementing the treaty, adding to concern that Moscow may have decided not to be bound by its provisions.

Thus the new missile test notification has taken on special interest here. Officials say they are reluctant to draw too many conclusions at this point, since the notification was just given to the State Department. But one senior official said it was "the first good news" about SALT in a long time.

The upcoming tests are of a special nature. In previous arms agreements, both countries have provided notice of flight tests, which carry their long-range missiles into target areas in remote ocean regions.

Under the new treaty, however, provisions require advance warning of tests in which a number of missiles are fired within a short period of time over land areas.

In effect, this applies only to the Soviets, who sometimes test-fire their missiles from launch sites in the Southwestern U.S.S.R. over vast reaches to the Kamchatka Peninsula in Soviet Asia.

The new requirement involves notice of tests in which more than one missile is in the air at one time, and the Soviets are understood sometimes to fire a second missile before the first one lands.

The upcoming tests are the first of their kind since the Vienna agreements were signed last June, sources said.

Notification of the planned firings is understood to have been made via the U.S. Embassy in Moscow rather than at the Geneva talks.

The U.S.-Soviet discussions in Geneva involve what is called a Standing Consultative Commission, set up initially by the two nuclear superpowers to discuss implementation of the first SALT agreement in 1972 limiting intercontinental-range missiles and antimissile defenses. This commission has met periodically since then.

Sources said the current round of talks in Geneva has just ended and, while the Soviets stuck to their policy of not discussing the SALT II pact, the atmosphere at the talks did not suggest any would-be collaspe of the SALT process. The Geneva talks also apparently survived the raising, by U.S. delegates, of the Afghanistan invasion as an issue complicating SALT, according to reports circulating here.

The first SALT pact froze the number of long-range missiles and bombers in each superpower's aresenal to levels existing at the time, a plan that permitted the Soviets more missiles than the United States because Moscow had more under construction.

The new pact is meant to place ceilings on those forces to make their numbers equal and to limit certain kinds of weapons specifically.

The Carter administration, while deferring action on SALT for the time being, has cocnsistently argued that the new pact is actually in the U.S. interest, despite other disputes with Moscow, because it would mean a reduction in the existing Soviet forces.