Yuri Andropov, chief of the KGB security police for the past 15 years, was elected to the powerful Soviet Central Committee Secretariat today in one of the most significant shifts in the Kremlin leadership in recent years.

The choice of the 67-year-old politician to fill a post vacated by the recent death of chief Kremlin ideologist Mikhail Suslov clearly widened Andropov's responsibilities and strengthened his position as a possible successor to Soviet leader Leonid Brezhnev.

The elevation of Andropov came at the end of a one-day meeting of the Central Committee, which unanimously approved Brezhnev's special food program for the 1980s.

In his speech at the session, Brezhnev talked about "big losses" of harvested crops and meat and milk products due to low efficiency, inadequate storage facilities, "an insufficient level of all-round mechanization" and "poor exploitation and low quality of many types of agricultural machinery."

But the 75-year-old Soviet leader said the new food program would pour massive amounts of money into the villages. He said that approximately one-third of all Soviet capital investments in the period of 1986-90 will go to the agricultural sector.

Apart from reflecting a broad consensus for decisive action to improve the food situation, however, the Soviet leader's speech did not provide any specific details to suggest a dramatic change in Moscow's approach.

Western diplomats said they expected Andropov to take over Suslov's position as ideologist, which would give him great influence over personnel matters as well as foreign policy.

The diplomats said the main loser in the appointment appeared to be Konstantin Chernenko, Brezhnev's long-time chief of staff, who has been Andropov's main rival for Suslov's position.

Chernenko, 70, remains as Central Committee secretary in charge of its general department. He appears to have a narrow base of support apart from his personal closeness to the party leader.

Apart from Brezhnev, Andropov and Chernenko, the only senior figure who is both a Central Committee secretary and Politburo member is Andrei Kirilenko, 75. He is described as being seriously ill and not likely to emerge as a top contender for the job of party general secretary, which Brezhnev has held since October 1964.

The 11-member Secretariat directs the work of the Communist Party apparatus on a day-to-day basis, while the Politburo sets policy for the party.

The Central Committee also promoted one of its secretaries, Vladimir Dolgikh, to the status of alternate member of the Politburo. At 57, Dolgikh is described as one of the most intelligent and educated persons in the leadership.

Brezhnev said that the government plans to allocate the equivalent of $230 billion in this decade for building and road construction in the rural areas.

"This is a big sum even by our standards," he said. But, he added, "this is a big policy decision aimed at eradicating distinctions in social conditions between town and countryside."

He also announced that wholesale prices paid by the state to purchase grain, meat, vegetables and other products from collective farms would be increased as of Jan. 1. The program, he said, envisages organizational changes to improve productivity and reduce waste.

Noting that the Soviet Union had been compelled to step up purchases of foreign grain, meat and other commodities "in the interest of the people," Brezhnev announced that Moscow intends to reduce such practices in the future.

The draft program, Brezhnev said, "proceeds from the need to reduce imports from the capitalist countries. The interest of the country demands that we should have adequate food and fodder resources of our own,which would put us beyond the reach of chance."

In a clear reference to the United States, Brezhnev said the Soviet Union will "never put up" with certain countries trying to use "grain sales" as a means of "political pressure."

Brezhnev's speech, which was read over Moscow television and then distributed by the government news agency Tass, did not include details of the food program. The Soviet leader talked in general terms about the reasons for difficulties.

He conceded that "the demand for meat and dairy products is not yet met, there is a shortage of vegetables and fruits and disruption in trade of foodstuffs occurs in a number of regions."

It was too early to make a full assessment of the government's food program, which would require careful study. The program has not yet been published.

In general, however, Brezhnev's speech appeared to reflect growing concern about the country's ability to feed itself but did not suggest any remedies that would involve bold departures in Moscow's economic thinking.

The program envisaged huge capital investments in the agricultural sector and cash incentives to stimulate collectivized farmers, but the measures seemed to be planned in the context of the existing centralized economy.

Despite its professed political will to seek solutions to the food problem, the Soviet leadership has yet to demonstrate the strength and ability to put in effect changes it wants to see.

Brezhnev appeared to defend past policies by asserting that the decisions of a Central Committee plenum in 1965--during the first year of his rule--remain the basis of the party's agricultural policy. He called it "a correct policy from which we did not depart and will not depart."

He talked about increases in absolute production figures and asserted that difficulties were caused in part by a massive exodus of the rural population into the cities.