Supporters of the public service employment (PSE) program began organizing a rescue effort yesterday, after the House slashed the bill so deeply Wednesday night the leaders yanked from the floor and postponed further action until mid-September.

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) acknowledged yesterday that the bill won't come up again until after the House returns from its recess Sept. 6, adding that he thought big-city mayors did a poor job of marshaling votes for the controversial measure.

"Let them regroup," said O'Neill, according to wire service reports.

The House, spurred by a general budget-cutting mood and by reports of scandals in the PSE program, slashed 100,000 PSE jobs from the 725,000 proposed in the bill extending the Comprehensive Employment and Training Act.

The House voted additional restrictions and appeared in the mood for possible further cuts before O'Neill took the bill off the floor. Supporters feared even more damage, in part because of a prior agreement not to continue discussions too late, and also because of an accusation by Rep. Ronald V. Dellums (D-Calif.) that some members were "slightly intoxicated."

Originally, it was planned to resume debate in a day or two, but congressional sponsors of the bill, hoping for more time to round up votes, have won a postponement until September.

They say they believe they can stem further cuts, but only if the groups lobbying for the bill mount an intensive campaign over the next few weeks.

One lobbyist said yesterday that the postponement was providential because "in the mood they were in they might have wiped it out."

Now, representatives of the U.S. Conference of Mayors, the labor movement, the National Association of Counties, the National League of Cities and the National Governors Association as well as the Carter administration are mapping strategy for a major effort to shore up support for PSE both in the House and Senate.

President Carter has asked for about $11 billion for CETA for fiscal 1979. Part of the money is for employment training and placement, but about $6 billion is intended to keep the number of federally funded public service jobs at about 725,000.

The program has been sorely hurt in the public mind by reports that politicians have put their relatives on the PSE payroll, given out jobs through the political clubhouses and substituted the federal money for outlays the cities should have made themselves.

The House vote to slash the PSE portion by 100,000 jobs on Wednesday night was substantial - 221 to 181.

The bill also faces some problems in the Senate, where there is a possibility it will come up this month, perhaps next week.