A Senate committee yesterday opened the first hearings on legislative proposals to limit television networks' projections of presidential election results before polls close in the West, making voting hours uniform across the country, and move presidential elections to Sunday.

Richard M. Nixon, Gerald R. Ford and Jimmy Carter, the nation's last three chief executives, all expressed interest in Sunday elections as a way to get more people to vote. Rep. Mario Biaggi (D-N.Y.), author of the proposal, introduced letters from each of the former presidents.

None of the three came flat out and endorsed Sunday elections but each said the idea deserved airing.

"I think your suggestion with regard to Sunday voting has a great deal of merit," Nixon wrote. "Constructive steps that can be taken to increase voter turnout should receive very serious consideration."

The proposal, which would also set up uniform voting hours around the country, is aimed at two problems: low voter turnout and the television networks projecting presidential election results while polling places are still open in the West.

Sen. S. I. Hayakawa (R-Calif.) who supports the plan, said last November many voters in his state "went home without having cast a ballot for their next president" because "they heard the broadcast networks proclaim a winner in the presidential race before they had a chance to vote."

"Voters in the western states believed that voting was a useless exercise," he told the Senate Rules Committee. "They had been disenfranchised by a system that allowed an election to be called while the polls were still open."

Hayakawa has also proposed that election officials be barred from releasing any vote results until all polls are closed around the country. Predictably, news executives from the major television networks strongly opposed any attempt to limit their ability to project election results. They also insisted such projections did not influence the election.

William J. Small, president of NBC News, called Hayakawa's proposal "distressing and potentially dangerous. Broadcast projections have never been demonstrated to have any measurable effect on either voter turnout or voter choice," he said.

I would like to go on record as expressing the vehement opposition of CBS News to any proposals which would require any news organization to suppress information in its possession, or would deny to us access to any information that would otherwise be available," said William A. Leonard, president of CBS News.

Richard Wald, senior vice president of ABC News, argued that "our free press traditions" and First Amendment freedom of press provisions require Congress to avoid restricting news coverage.

But the League of Women Voters and 32 other groups urged the networks to voluntarily refrain from projecting the winners of elections. Such projections, league president Ruth J. Hinerfield said, "have no positive purpose in the election process."

California Secretary of State March Fong Eu testified that voter turnout dropped suddenly last November after NBC projected Ronald Reagan the winner of the presidential election at 5:15 p.m. California time.