Rep. Richard A. Gephardt (D-Mo.), chairman of the House Democratic Caucus, yesterday accused President Reagan of being a "bystander president" who has failed to develop a national consensus that would support the painful budget cuts necessary to significantly reduce the federal deficit.

Gephardt said that until Reagan makes known his budget-cutting decisions, Democrats will make no proposals.

Sen. Pete V. Domenici (R-N.M.), chairman of the Senate Budget Committee, said he could "guarantee" that Republicans would come up with "a major deficit-reducing package" that cuts about $50 billion from spending for fiscal 1986. This would be close to the $54 billion that the administration has said would cut the deficit down to 4 percent of the gross national product.

Gephardt and Domenici appeared on ABC's "This Week With David Brinkley."

"We've got a bystander president who's not leading the country," Gephardt said, "and until he does you're not going to resolve the problem."

Gephardt said the administration has the burden of acting first. "They won the presidency," he said, " . . . It's clear they have the obligation to serve up a budget . . . . "

Gephardt said that when House Democrats act on the budget, they will consider all options, including cutting defense spending and Social Security and raising taxes.

Domenici said that while Senate Republicans do not yet have a plan, "we're going to produce a major deficit-reduction package. We're hoping it will be something the president can support because we've taken his plan and built on it."

Domenici said small deficit reductions will not be acceptable. "There's no use talking about saving $20 billion," he said. "We've got to save about $50 billion in the first year and that's got to naturally grow to over $100 billion in the third year."

Office of Management and Budget Director David A. Stockman, appearing on the same program, acknowledged that the budget Reagan is to submit Feb. 4 is not expected to reach the announced $100 billion deficit-reduction goal in three years.

Because 22 Republican senators will be up for reelection in two years -- 40 percent of the Senate GOP -- it has been suggested that Republicans will not be eager to cut popular programs.

But Domenici said, "If you make the hard votes then and the American economy is humming when these 22 are up, the people will not remember these votes."