When he took charge in the Kremlin last November, Yuri Andropov told the Soviet people that he had no ready "recipe" for curing the country's economic and social ills.

This week, however, Andropov came up with a recipe--making a decisive break with the past and offering a broad program of modernization based on hard work, discipline, financial incentives and a whiff of democratization.

Whether the combination is sufficient to break the economic immobility gripping the country--or whether Andropov eventually may decide on even bolder measures--is as yet not clear. Soviet society moves slowly, and its huge bureaucracy is renowned for its capacity to resist change.

But it would be a mistake to dismiss quickly the plans of this gaunt, shrewd and calculating man who served for 15 years as chief of the KGB secret police and who managed with unerring maneuvers to achieve preeminence in the ruling Kremlin council in less than one year.

One problem for Andropov is his health. Foreign visitors reported recently that he looked physically weak and not the kind of man to shake up the country. But they also said he was lucid and very intelligent, in full control of facts and figures, "like a computer in the precision of word and gesture."

It was clear from his speech to the Communist Party's Central Committee this week that Andropov's main concern is the economy. Even the foreign policy issues that he touched upon--Moscow's relations with the United States, the Third World and socialist countries--were placed in an economic context

While he generally followed his predecessor Leonid Brezhnev in foreign policy, Andropov introduced a few subtle modifications. He never mentioned the word "detente," but rather used the phrase "peaceful coexistence" that was used by Soviet leaders before the period of Soviet-western detente.

This suggested that Andropov would be more wary of the United States than his predecessor and that he views the evolution of U.S. diplomacy under the Carter and Reagan administration as one of "permanent hostility" toward Moscow.

In distancing himself from Brezhnev's domestic policies, Andropov followed the Byzantine way in which new Kremlin leaders go about disposing of their predecessors' programs. He had Konstantin Chernenko, Andropov's one-time rival and the closest political associate of Brezhnev, deliver the keynote address, which sharply criticized the policies of the past two decades.

When Andropov took to the rostrum at the Central Committee meeting, he condemned many former policies as badly flawed and unrealistic without attacking his predecessor personally.

He said the economy he inherited was being run in an "irrational" way, that the Soviet Union was not building communism but was "at the beginning" of a long phase of "developed socialism," and that the country had reached the point where deep changes in the economy have become "inevitable."

Without referring directly to the American challenge but clearly having it in mind, he said that such changes were not "just our wish" but that they were necessary and there "is no way of avoiding" them.

That his broad program for changes was adopted by the Central Committee as the party's "platform" until the next party congress suggested that a majority within the elite shared Andropov's assessment of the internal and foreign situations.

While much attention was focused on his election to the presidency, a largely ceremonial job, Andropov had acted as the unchallenged leader since he assumed the post of general secretary of the party last November.

Foreign observers are divided in their assesssments of Andropov's political strength. Nobody questions his personal authority, but there are disagreements as to the extent of his control over the Politburo.

Some observers say that the fact that western predictions of a major reshuffle of top positions did not materialize should indicate that Andropov was not able to bring his own men into the Politburo. Others contend that most Politburo members who were formerly closely associated with Brezhnev now accept Andropov's leadership.

While there were no sweeping changes, some important shifts were made, bringing to the fore people likely to figure in the next succession.

Grigori Romanov, 60, who is a member of the Politburo, was brought from Leningrad to Moscow and made a secretary of the Central Committee.

He and Mikhail Gorbachov, 52, a Politburo member, who is also a secretary of the Central Committee, and Gaidar Aliyev, 60, a former KGB officer, who was made a full member of the Politburo under Andropov and appointed first deputy premier, are viewed here as potential leaders in the post-Andropov period.

Brought from the Krasnodarsk region to Moscow was Vitaly Vorotnikov, 56, who was named an alternate Politburo member. He is expected to become premier of the Russian Federation, the country's largest republic, replacing Mikhail Solomentsev, 70, who was appointed head of the party's control commission.

Solomentsev, not a Brezhnev ally, was expected to turn the control commission into a tool for fighting party bureaucracy. The commission had become dormant under his predecessor, Arvid Pelshe, who died last month at age 84.

In addition to Vorotnikov, other rising figures are alternate Politburo members Eduard Shevarnadze, 55, and Vladimir Dolgikh, 58.

While there is no doubt that Andropov intends to make changes in the economic field and in the way the bureaucracy operates, such changes are bound to be unsettling to the entrenched middle- and low-level party and government bureaucrats.

Thousands of middle- and low-echelon officials have been removed during the past six months. But the total number of officials runs into millions and it will take much more to get the party apparatus to respond.