Disgruntled leaders of the Democratic Party from urban areas around the country complained bitterly yesterday about 63 House Democrats who defected Thursday to support President Reagan's budget cuts, but agreed that they could do nothing to discipline them until the 1982 elections.

"Out job is to beat Republicans and hold them accountable," said Charles T. Manatt, the new chairman of the Democratic National Committee, in explaining the lack of action despite the griping about Democratic defectors that filled the air at the meeting of the party's executive committee.

"I will be visiting with [House] Democrats individually and urging them to support the Democratic position on the tax bill," Manatt said, "but I don't think we can come in here the day after a vote and take [punitive] action about a vote they have already cast."

That statement was not challenged by any of the 26 party leaders who met for three hours yesterday, but neither did it inhibit them from voicing their frustration with the shellacking Reagan gave the Democrats in the House.

"Those Democrats ought to recognize in some way that we are very, very unhappy with them," Mayor Lee Alexander of Syracuse said. "I hope we can make our displeasure and shock known."

Earlier, his fellow mayor Richard G. Hatcher of Gary, had asked Eugene Eidenberg, the former Carter White House official named by Manatt as executive director of the committee, what the party intended to do about the 63 defectors.

"I don't think we have a position," Eidenberg said, "but my own political judgment is that those people who chose to vote against the interests of the country will begin to reap the whirlwind."

Jerry English, a Summit, N.J., Democrat, said the rout showed "We lack discipline and we lack leadership in the House and we better learn from it."

In its only major action, the executive committee endorsed "in general" Manatt's proposal to restructure the 1982 mini-convention into a smaller, less expensive meeting than the 1974 and 1978 versions.

With some members complaining that the changes would violate the mandate of the 1980 convention, the executive committee endorsed the plan to have the 1982 delegates chosen by the state and national committees, rather than elected by grass-roots Democrats.

The Democratic National Committee is expected to approve the proposal at its meeting in Denver next month.