Plagued by mercurial weather, the Soviet Union appears to be heading toward its fourth bad grain harvest in succession even as it copes with shortfalls of meat and vegetables that result in part from managerial problems.

Official indicators suggest an even leaner outlook for the already pressed Soviet consumer. Meat production for the first half of this year has declined by 2 percent from last year's disappointing levels and shortages of fruits and vegetables have been obvious this spring and summer.

The Soviet media has indirectly reported serious deficiencies, focusing on the shortage of containers and refrigerated vehicles and poor transportation facilities. The newspaper Sovyetskaya Rosiya gave instances of collective farmers killing young cattle to meet state production quotas on meat.

Pravda, the Communist Party newspaper, gave the most devastating picture to date of losses due to transportation difficulties.

A dispatch from the southernmost section of Azerbaijan--a subtropical area which supplies fruit and vegetables for Moscow, Kiev and other cities--said that vegetable deliveries have declined 33 percent in April and May compared to last year's figures. It said that while the Lankoran area is able to deliver 4,000 tons of vegetables daily, it sent only 800 tons per day during the two-month period.

According to Western estimates, the grain harvest again is expected to be 40 million to 60 million tons below target--meaning Soviet grain buyers can be expected to shop the world markets to make up for the shortfall.

For experts, the most significant signal suggesting just how poor the grain harvest may be was the publication last weekend of figures on land devoted to grain.

This year's total grain area of 306 million acres is the smallest since 1972. This means that the Soviets put less grain in the ground than in previous years and could not expect a big harvest in any case. The grain area in 1978 was 316 million acres. The spring harvest was adversely affected by weather conditions, including severe drought in an area ranging from the Volga River to the Urals and on to the huge province of Kazakhstan.

Since then, however, heavy rains, hail and high winds have hampered field work in the southwestern parts of the country and particularly in the Ukraine, according to Western specialists.

In Soviet Georgia, more than 100,000 sheep and goats and more than 25,000 pigs were killed in recent floods, according to an official report, while thousands of acres of vineyards and tea plantations were ruined by hail.

The value of lost grape production alone was said to be in excess of $220 million.

Rains are said to have helped some crops, such as corn and sunflowers, but their output is not expected to exceed last year's levels.

According to diplomats, the Soviets have not yet shopped abroad for grain this year. Elsewhere, production is expected to be at record levels. Argentina, Canada and Australia all have abundant supplies of wheat.

It is speculated here that the Soviets are waiting for the price to drop before moving into the markets.

Since last summer, meat products, butter and milk have been rationed in various ways in the Soviet Union. How another poor harvest is going to affect the government's food program, launched in May to improve the consumers' situation, is unclear.

The U.S. Department of Agriculture's latest estimate on the Soviet grain harvest is "170 million tons, plus or minus 10." Since the 1978 grain harvest of 238 million tons, the Soviet harvests have been shrinking, with shortfalls from production targets of between 40 million and 50 million tons.

The latest figures and Western estimates suggest the continuation of structural weaknesses in agriculture, including the problem of incentives, poor agricultural and transportation equipment and negligence.