Partial returns in yesterday's statewide elections in this ethnically divided northeastern state of Assam showed Indian Prime Minister Rajiv Gandhi's ruling party running behind a new party formed by native Assamese.

Returns available tonight showed the Assam People's Council leading in 53 state assembly races and Gandhi's Congress (I) party leading in 30, according to The Associated Press.

At stake were 125 seats in the state assembly and 14 in India's Parliament in a contest seen as crucial for Gandhi's political control over the state. In September, his party lost by a landslide in the northern state of Punjab to the Sikh Akali Dal Party.

With more than 70 percent of the 9.9 million eligible voters in this oil-rich, tea-growing state casting ballots, a record, the manual counting of returns was going slowly.

Officials said voting had been generally peaceful. About 200,000 riot troops and police guarded centers where election workers began counting votes this morning.

Gandhi called the midterm state elections as part of a settlement to end six years of bloody turmoil between native Assamese and immigrants from neighboring Bangladesh that had prevented elections for parliamentary seats in 1980 and 1984.

Most native Assamese boycotted the last state election, in February 1983, when Gandhi's party won 90 seats. Only 17 percent of those eligible voted in that election, and more than 3,600 people died in election-related violence.

The mainly Hindu natives of Assam complain that millions of immigrants, mostly Moslems from neighboring Bangladesh, threaten to make them a minority in their own homeland. Bengali immigrants now make up about 40 percent of the state's 22 million residents.

Gandhi reached a settlement last August with the anti-immigrant forces, but the accord has brought new bitterness and fear.

Under the accord, Gandhi agreed to hold new state elections, expel all illegal immigrants who entered Assam from Bangladesh after 1971, and disenfranchise for 10 years those settlers who came between 1966 and 1971, after which they are to become full Indian nationals.

Another new party, the United Minorities Front, opposes the accord.