Kremlin 'conventions': Will new heir apparent emerge?

Promotion of a stocky mining engineer largely unknown outside the Soviet Union . . . . A new plan to develop Soviet energy resources . . . . The future of Soviet leader Leonid Brezhnev . . . . Clues to how the Kremlin intends to grapple with the huge but ailing Soviet economy over the next five years . . . .

All are at the center of speculation by full-time Kremlin watchers here on what flow from party and government meetings to be held in the Kremlin June 23 and 24.

Yet Kremlinologists in the Western diplomatic community stress the limited nature of their knowledge. Ever since 1917, a heavy curtain of secrecy has hung over the inner workings of the Kremlin, blocking the best outside efforts to peer in.

No one here doubts that the meetings are significant, given the shortages of energy, the below-target performance of large sectors of the economy, and the advanced age of the Communist Party's 14-man Politburo.

Yet analysts stress caution, "It is all very, very important," comments one of the hardest-working Kremlinologists in Moscow, "but we are very, very ignorant."

The party Central Committee is expected to meet June 27 behind closed doors. The Supreme Soviet (nominal legislature) meets June 28 to ratify party decisions.

Diplomats are focusing on former mining engineer Vladimir Dolgikh for two reasons:

* He is in day-to-day charge of heavy industry for the secretariat of the Central Committee, and he appears to be heading the drive to develop a new plan to save energy and to find more of it.

There is speculation that he may be promoted to nonvoting (alternate) member of the Politburo, signaling both his standing in the party and the emphasis the leaders put on the fields in which he specializes -- especially energy.

* Mr. Dolgikh was unusually prominent at a recent session of the supreme soviet of the Russian Federation, biggest of the 15 Soviet republics. With Mr. Brezhnev, Premier Alexei Kosygin, ideologist Mikhail Suslov, and Brezhnev heir apparent Andrei Kirilenko all absent, Mr. Dolgikh sat in the next senior spot on the dais.

He has been prominent among speakers at various meetings on energy reported recently. So has Mr. kirilenko, who presided over key meetings of party officials in Moscow in recent weeks: one on energy, another on machine-tool and other sectors of heavy industry.

Lately the press has been devoting much space to energy problems, stressing the need to build machinery that is energy-effcient and the urgent need for new sources of energy. General policy is to press ahead with nuclear power generation and coal as alternatives to oil.

In contrast to the United States, industry is the big waster of fuel here. Most city apartments are heated efficiently by gas-fired steam boilers; private autos have only just reached the number on US roads in 1920. Vast amounts of energy are transported from oil and gas fields in Siberia and the east to the energy-short western USSR.

As for Mr. Brezhnev himself, he has given no clues as to who might succeed him. (Most Westerners believe Mr. Kirilenko would be the stopgap leader in an emergency.)

He could decide to give up his post as party leader and remain chief of state , thus attempting to become the first party leader to step gracefully into retirement.

Today he seems to be in good health after years of chronic difficulties. He will be 74 on Dec. 19.

His precise position in the balance of forces on the Politburo is a mystery. He is seen as a consummate consensus man, never allowing himself to be isolated in a minority for long, unhappy at the crumbling of the detente he worked hard to achieve but also supporting those who favored the invasion of Afghanistan.

Some ask whether his position might have been weakened along with the detente with which he is identified. Others ask why none of the 11 ministers and senior officials he criticized by name is a scathing attack on economic shortcomings a year ago have not yet lost their jobs. The implication is that he is unable to ram through at least some of his own desires.

The Central Committee may announce the dates and speakers for the 26th party congress early next year. The congress, held once every five years, will outline economic plans for 1981 to 1985.