The White House has accepted Soviet proposals for a more intensive schedule than expected at the Vienna summit meeting between President Carter and Soviet President Leonid Brezhnev three weeks from now.

The planned schedule has generated cautious optimism that meetings with the 72-year-old Soviet leader will be much more than an exchange of formalities.

According to what is described as an agreed schedule, Carter and Brezhnev are to meet for five working sessions June 16, 17 and 18, as well as dinner meetings on two nights and the ceremonial signing of the new strategic arms limitation treaty (SALT II). The working sessions are expected to last about two hours each.

The schedule proposed by the Soviets is taken as a hopeful sign, but by no means a certainty, that Brezhnev will be ready for relatively productive discussions.

Adding to the mild optimism are reports from Belgrade that, after a slow and rocky start, Brezhnev showed physical capacity and a sense of command during the Kremin meetings a week ago with Yugoslav President Tito.

The yugoslav reports were almost as upbeat about Brezhnev's condition as the Paris reports on the Soviet-french summit meeting six weeks ago were downbeat. President Valery Giscard d'Estaung reportedly found Brezhnev capable of only brief concentration. Some Soviet specialists here, however, consider both reports exaggerated and suggest that Brezhnev's true condition is somewhere in the middle.

Another hopeful sign - although something of a puzzling one - are reports that Brezhnev will make a three-or four-day visit to Hungary late this week. There is no indication why the Soviet chief feels it necessary to undertake a taxing journey just before the Carter summit. U.S. sources believe that part of the reason for the Hungarian trip - though probably not the major reason for it - may be a desire to show the world and possibly even doubters in the Soviet leadership that Brezhnev is vigorous enough to meet with Carter.

Brezhnev is reported to be suffering from a long list of physical ills ranging from circulatory disorders to emphysema and even ill-fitting teeth. There is a consenus among Soviet watchers here that his fitness has peaks and valleys, but that each year the peaks become lower and the valleys deeper.

U.S. officials said there is no doubt that Brezhnev is the man in charge at the Kremin despite his infirmities. A recent study by a U.S. intelligence organization concluded that, despite suggestions to the contrary three years ago, Brezhnev is likely to remain as at the top of the Soviet hierarchy as long as he is physically able.

The recent study concluded that he is unlikely to retire, even after the successful completion of the SALT II accord on which he has staked much prestige and which is viewed by many as the potential capstone of his leadership. Some evidence has been accumulated that contenders for position in the successor leadership would like to see Brezhnev remain in place as long as possible - a desire that's believed to coincide with Brezhnev's own inclinations.

In addition to Brezhnev and Foreign Minister Andrei Gromyko, U.S. officials are hoping that Carter and his summit team will be able to meet with some other high-ranking Soviets, particularly those in the miltary field.

Secretary of Defense Harold Brown and Gen. David C. Jones, chairman of the Joint Chiefs of Staff, have been named to accompany Carter to Vienna, along with Secretary of State Cyrus R. Vance and presidential assistant Zbigniew Brzezinski.

The presence of Brown and Jones is considered appropriate for a meeting whose central purpose is the strategic arms accord, and it also may be a bid to encourage the presence of Soviet Defense Minister Demitri F. Ustinov, Gen. Nikolai Ogarkov, the deputy minister of defense and the senior career miltary man, or some other top uniformed officials.

In the first month of his presidency, Carter privately backed a plan for periodic meetings between defense ministers and top miltary officers of the two nations to improve understanding and avoid dangerous and costly misunderstandings. This idea, like Carter's plan for regular meetings of himself and Brezhnev, evaporated early.

The Soviets insisted, starting early in 1977, that a summit meeting should not be held until a SALT agreement was ready for signing, and the pace of the negotiations proved to be far from tortous than either side expected. In three weeks Carter will have his first chance to "get my hands on Brezhnev," as he often expressed a desire to do in the interest of dispelling strains and tensions. The chances are good that he then will suggest regular meetings of the top political leaders, and perhaps of the miltary leaderships as well. CAPTION: Picture, LEONID BREZHNEV . . . agrees to five sessions with Carter