DISPUR, India (AP) _ Youths danced in the streets and exploded firecrackers today, celebrating early returns from Assam state elections showing Prime Minister Rajiv Gandhi's Congress Party losing to a new party formed by native Assamese.

According to early returns from Monday's balloting, the new Assam People's Council was winning in 51 state assembly races and the Congress Party was ahead in 31.

Only four results had officially been declared by 7:30 p.m., and all four had gone in favor of the Assam People's Council.

The council's 34-year-old president, Prafulla Mahanta, won in two districts. Candidates may run from more than one district, but can only represent one. Mahanta will have to resign from one district.

Mahanta was declared the victor in his home district of Nowgong and the adjacent district of Koliabor, south of here. In Nowgong, he soundly defeated State Education Minister Mukund Sarma.

In another race, a Gandhi ally who is the state's top official, Chief Minister Hiteswar Saikia, was trailing his opponent, Tanu Kanwar, by 41 votes in his home constituency of Nazira, near the border with Nagaland.

The state legislature has 126 seats, but one race was postponed because of the death of a candidate. Fourteen seats in the Indian Parliament also were at stake.

More than 70 percent of the 10 million eligible voters cast ballots, the largest turnout in an Assam election since Indian independence in 1947.

Chief election officer P.C. Misra said one election official was shot and wounded by an unidentified man Monday evening. The gunman escaped.

He said unidentified groups snatched ballot boxes and ran away at five voting stations Monday. Balloting at those stations resumed today, he said.

The Assam People's Council led in Assam's capital, Dispur, and the adjacent city of Gauhati. The party received all the votes cast at three booths in Gauhati's western constituency, officials said.

More than 200,000 riot troops and tear gas squads guarded centers where elections workers began counting votes by hand this morning.

Large crowds supporting the Assam People's Council chanted anti-Congress Party slogans and cheered each time party members announced a new trend over loudspeakers at the counting centers.

Gandhi called the midterm state elections as part of a settlement to end six years of bloody strife between native Assamese and immigrants from neighboring Bangladesh.

The turmoil forced cancellation of elections for parliamentary seats in 1980 and 1984. Most native Assamese boycotted the last state election in February 1983, in which the Congress Party won 90 of the legislature's 126 seats.

Only 17 percent of eligible voters participated in that election, and agitators blocked voting in 18 constituencies. More than 3,600 people died in election-related violence.

The mainly Hindu natives of the oil-rich, tea-growing state complain that million of people, mostly Moslems, have entered the state illegally from Bangladesh since the 1950s and threaten to make them a minority in their own homeland. Bengali immigrants make up about 40 percent of the state's 22 million residents.

Under the Aug. 15 settlement, Gandhi agreed to hold new state elections, expel all illegal immigrants who entered Assam from Bengladesh after 1971, and disenfranchise for 10 years settlers who came between 1966-71.

Student leaders of the anti-immigration movement formed the Assam People's Council after they signed the settlement.

The party's top leaders, Prafulla Mahanta and Bhrigu Phukan, were ahead of their Congress Party rivals in the constituencies of Nowgong and Jhalukbari. Congress Party candidates led in four constituencies in western and southeastern Assam.

Another newly established party, the United Minority Front, was ahead in nearly two dozen districts.

The front was founded to oppose the settlement, dealing the Congress Party a serious setback by splitting the governing party's traditional constituency - Bengali immigrants.