The confusing new Soviet election system could pit human rights activist Andrei D. Sakharov in a campaign battle against a member of the ruling Politburo and another Communist who ran afoul of party leaders.

"I believe a more democratic mechanism of nominating candidates is needed," said Sakharov, who was selected both as a Moscow district and at-large candidate for the new 2,250-member Congress of People's Deputies.More than 900 people jammed into a meeting Sunday that unanimously nominated the Nobel Peace Prize-winning physicist for the at-large post in the March 26 elections, an activist said. At least 500 people waited outside the hastily organized session at the House of Filmmakers.

Yuri Mityunov, a participant, said a city Election Commission member told the meeting that Politburo member Vitaly I. Vorontnikov and Moscow's deposed Communist Party leader, Boris Yeltsin, were running for the same at-large seat.

The possible campaign battle among Sakharov, Vorontnikov and Yeltskin and the scramble among thousands of candidates nationwide depends on twists and turns in the new political system charted by President Mikhail S. Gorbachev.