If the Reagan administration carries out plans to close an 800-bed facility for the homeless Aug. 31, its residents will be forced to sleep in parks and abandoned cars because there are not enough beds in other District shelters, activist Mitch Snyder told two congressional subcommittees yesterday.

"Small shelters exist only in the pointy little heads of bureaucrats," said Snyder, leader of the Community for Creative Non-Violence. Because there are fewer than 150 beds, and nearly all of them occupied, in other District shelters, he said, "the solution is the streets."

Snyder's testimony came during a five-hour public hearing before the House's public building and grounds and its housing subcommittees on a bill by Rep. Kenneth J. Gray (D-Ill.) that would authorize the federal government to spend $10 million to renovate CCNV's shelter at 425 Second St. NW.

The public building subcommittee, which is considering Gray's bill, is not expected to vote on it until after Congress' upcoming recess.

On Wednesday, the U.S. Department of Health and Human Services announced it plans to close the squalid shelter, one of the nation's largest, by the end of the month, even though it is unclear where its residents would go.

CCNV has filed suit in U.S. District Court here to keep the shelter open and force the federal government to make $10 million in repairs. Two days before last November's election, President Reagan promised to transform the facility into a "model" after Snyder agreed to end a 51-day hunger strike that had attracted worldwide attention.

A hearing in the case is scheduled today before U.S. District Judge Charles R. Richey. At previous hearings, Richey has said he is concerned about what might happen to residents if he grants the government's request to close the facility, which it regards as a health hazard.

HHS, which ended an unusual alliance with CCNV in June and originally planned to close the shelter July 10, had hoped the District would assume responsiblity for shelter residents. City officials, however, excluded from the deal between Reagan and CCNV, have consistently refused to make such commitments. They have said that caring for the 800 residents for one year would cost triple the $2.7 million the federal government has offered.

At yesterday's hearing, HHS Undersecretary Charles D. Baker and Rep. Clay Shaw (R-Fla.) blamed the city for failing to assume responsibility for the CCNV residents.

"It was certainly our expectation . . . that the District government would be involved in the operation of this shelter," said Baker, who added that he hoped that closing the facility would "bring forth the development of adequate alternative shelter."

Several lawmakers disputed Baker's contention that homelessness is a local, not a federal problem.

"I think it's outrageous" to blame the District, said Rep. Bruce F. Vento (D-Minn.) who added it was "regrettable the president has not seen fit" to keep his promise.

Snyder, who called federal officials "scum of the earth" and "piranhas who rip the flesh off the bones of the homeless," agreed. "The District never ever had a role in that building," he said. "They've been made a dumping ground and a scapegoat."