President Nicolae Ceausescu of Romania today underscored his country's move to achieve independence from the Kremlin by announcing the discovery of significant oil deposits in the Black Sea.

The news, which has been a closely guarded secret until now, was greeted with enthusiastic applause by over 2,500 delegates attending the 12th Congress of Romania's ruling Communist Party in Bucharest Ceasusescu, said the oil -- discovered with U.S. financial and technological assistance -- would help Romania reach its goal of complete self-sufficiency in energy by the end of the decade.

"We hope the deposits will be big and exploitable," he added, according to Western news agency reports monitored here.

Oil supplies are central to Ceausescu's insistence on Romania's right to purse its own idependent policies -- despite its membership of the Soviet bloc's trading organization COMECON and the Warsaw Pact defense alliance. Unlike other COMECON members, Romania does not rely on Moscow for its energy needs.

This has allowed Romania, a strategically placed Balkan country of 22 million people sharing an 830-mile common border with the Soviet Union, to follow a markedly different foreign policy course from its allies. Ceausescu has maintained good relations who both China and Israel and refused to increase Romania's financial contributions to the Warsaw Pact.

Earlier this year, however, Romania appeared to be in considerable energy difficulties as a result of a cutoff in oil supplies from Iran and dwindling production from its own main oilfields around the town of Ploesti in the south of the country. In 1978, for the time in many years, Romania imported more oil than the 94.5 million barrels it produced.

A dramatic energy conservation plan was announced by the Romanian government in August, but foreign observers expressed considerable skepticism that proposals for increased use of nuclear energy and even domestic windmills would make up the present deficit. "The president's speech provides the missing link in the jigsaw puzzle," commented a senior Western diplomat contacted in Bucharest.

Ceausescu did not reveal the exact size of the new deposits, but the Yugoslav news agency Tanjug reported that they were large enough to guarantee the country's energy self-sufficiency.

The first offshore drilling platform, financed in great part by a $2.4 million loan and credit guarantee package from the U.S. Export-Import Bank, went into operation in September 1978. Since then, however, there had been no official word of any discovery.

By saving the news until the party Congress, an important event for all Communist countries, Ceausescu is in effect advertising Romania's economic independence from the rest of the Soviet bloc. By contrast, a message sent to the congress from the Soviet Communist Party spoke of the benefits to be gained from close cooperation with the rest of COMECON.

The Soviet party, which is being represented in Bucharest by 80-year-old. Politburo member. Arvid Pelshe, also referred to the Warsaw Pact as "a reliable shield of the security of the socialist community." Foreign observers took this as an oblique criticism of Romania's half-hearted participation in the alliance and its refusal to allow Soviet troops to be stationed on its territory.

During his five-hour speech, the Romanian leader rejected any notion of closer military links with the Warsaw Pact, although he said that Romania attached special importance to relations with "our big neighbor, the Soviet Union." He called for a world-wide reduction in arms spending of 10 percent by 1985 and repeated an old proposal for a European disarmament conference.

Despite the oil finds in the Black Sea, an offshore extension of the Ploesti field it is clear that Romania is far from being free of energy worries. Under the new five-year plan, targets for industrial growth have been revised downward to 9 percent a year -- compared with 12 to 13 percent in recent years.

The plan also envisages the maintenance of a very high rate of reinvestment in heavy industry -- over 30 percent, which implies continued austerity for ordinary Romanians.