Yuri Andropov, the new Soviet leader, consolidated his authority today by taking a seat on the state Presidium and formally acquiring the right to act as head of state when the occasion requires.

Andropov, 68, who succeeded the late Leonid Brezhnev as general secretary of the Communist Party's Central Committee, is the most powerful political figure in the country.

His election to the 38-member Presidium of the Supreme Soviet, or parliament, a largely ceremonial body that is the collective state presidency, gives him the formal standing to deal directly with foreign leaders if he chooses.

The chairman of the Presidium is the nominal head of state. Each of its members, however, can fill in for the president. It was not clear whether Andropov would be made president at Wednesday's session of the Supreme Soviet.

Well-informed observers here believe that Andropov, after 11 days as party leader, commands sufficient support to win the presidency. There was speculation, however, that he may not want to take a position that involves a busy and time-consuming procession of ceremonial functions.

Brezhnev, who became the party leader in 1964, waited 13 years to assume the presidency, becoming the first Kremlin leader to hold both the top party and state posts. However, as a member of the Presidium, Brezhnev negotiated with president Nixon in 1972 and made numerous foreign visits during which he was treated as a head of state.

The Presidium has no significant authority and is composed of the leaders of various Soviet republics, representatives of various nationalities and prominent public figures. Among its members are Valentina Tereshkova, the first woman in space, and author Rasul Gamzatov.

Andropov was voted unanimously into the state Presidium by all 1,500 deputies meeting in a joint session of the bicameral Supreme Soviet at the start of the regular two-day fall meeting.

The delegates were seated in a vast neoclassical hall, about 350 feet long, in the Great Kremlin Palace, which once served as the residence of the imperial family during its visits to Moscow.

Andropov was nominated by Viktor Grishin, a member of the ruling Politburo. His election preceded government reports on the state of the economy and the proposed 1983 budget. When the chairman called for the "ayes," all hands were raised.

Although the post of president and membership in the Presidium are largely ceremonial, observers here believe that both give the party leader added flexibility, prestige and authority, particularly in foreign policy matters.

When Brezhnev assumed the presidency in 1977, Mikhail Suslov, the late chief ideologist, argued that a combination of the two positions was the most practical and flexible arrangement for the leadership. Nikolai Podgorny was dismissed to make way for Brezhnev.

The lineup of leaders seated in front of a statue of Lenin, about three times life size, did not provide any new clues about the balance of power in the Politburo.

The honored front bench was occupied by Andropov, Premier Nikolai Tikhonov, Politburo member Konstantin Chernenko, Marshal Dmitri Ustinov, the defense minister, and Foreign Minister Andrei Gromyko.

Arvid Pelshe, who at 83 is the oldest Politburo member and who was reported to have died, appeared at today's meeting, seated in the second row.

Nikolai Baibakov, the chairman of the State Planning Commission, outlined a draft economic plan for the next year, saying the government intended to reverse a slump in economic growth by stimulating a significant increase in labor productivity next year.

The plan called for industrial output to rise by 3.2 percent in 1983 compared to an expected 2.8 percent rise for this year. The 1982 figure is the lowest since the end of World War II.

Baibakov's report was remarkable for its lack of information about the state of the economy. He provided no details for the current Soviet grain harvest except to indicate that it is slightly better than the disastrous harvest last year.

Because figures for the harvest of 1981 were not published, it was not possible to reach any reasonable assessments except to conclude that overall farm output was sharply below the planned targets for the fourth year in a row.

Baibakov only said that agricultural output this year would have a value of $166 billion compared with the planned target of $182 billion. The target set for next year was put at $184 billion.

Finance Minister Vasily Garbuzov was equally obscure in outlining the next year's budget. He announced that defense spending would remain at 17.05 billion rubles, or $25 billion. Gabuzov had quoted the same figure for Moscow's annual defense spending for the past 12 years and this is generally believed to have merely symbolic meaning.

The real level of defense spending is far higher, with military allocations hidden in various other budgetary expenditures. For example, the spending "for the development of science" budgeted for the current year is $34 billion and much of that is believed to have been used on military research and development.

In contrast to previous years, neither Baibakov nor Garbuzov gave enough details to allow experts to calculate the real levels of defense spending.

It was made clear, however, that next year's planned growth would depend almost entirely on a rise in labor productivity.

It was also reported that oil production would rise next year to 12.38 million barrels per day from this year's target of 12.28 million barrels per day.

Both men made it clear that current economic performance was not good, presumably following the sharply critical line taken by Andropov in a speech to the Central Committee yesterday. U.S. Official Says Change Not 'a Great Opportunity'

Lawrence S. Eagleburger, undersecretary of state for political affairs, said yesterday that he personally does not believe that the change in Soviet leadership "means a great opportunity" for making dramatic changes in U.S.-Soviet relations.

Eagleburger, the third-ranking official of the State Department, was asked at a press conference for his assessment of Andropov. He replied: "Because a man wears a Western suit with cuffs on the pants does not make him a Western liberal."

While stressing that it is not yet possible to say what opportunities for change might result from Andropov's accession, Eagleburger noted: "He is out of the Soviet system, and we should not expect him to be anything more nor less than what he's come from."