Local governments and charitable organizations will be permitted to set up emergency shelters in some vacant federal buildings as part of an effort to provide desperately needed additional housing for the nation's growing homeless population, the Reagan administration announced yesterday.

The Department of Housing and Urban Development, which owns thousands of vacant dwellings throughout the country, the Department of Defense and the General Services Administration will make their unused property available, government officials said.

"The thing that excites me about the program is the potentially large number of federal facilities that are available," said Rabbi Martin Siegel, the coordinator of the plan and an adviser to the president's Office of Private Sector Initiatives.

Officials said it was not immediately known what specific buildings will be available in Washington or elsewhere, and that details of the arrangements will be worked out by local officials and their federal counterparts. The federal government will provide the buildings, but it will be up to local governments and volunteer organizations to equip and run the shelters.

"What we can do is provide space and provide it at a cost basis," said former Pennsylvania congressman James K. Coyne, recently named as Reagan's special assistant for stimulating privately sponsored social initiatives. "Different cities will have different ways of dealing with it," he said.

A White House spokeswoman said last night that the Defense Department, for example, is prohibited by law from providing space free of charge, but that department officials have told base commanders to be "as lenient as possible" in charging for heat and light for the buildings. That same leniency is expected from other government agencies, the spokeswoman said.

Local governments and housing authorities--not the charitable organizations--will be expected to pay for the utilities, the spokeswoman said.

The winter weather coupled with the faltering economy and cuts in local and federal social service programs have all swelled the ranks of those in need of emergency shelter. Unemployed middle-class and blue-collar workers have joined the more traditional homeless population.

Coyne said the shelter plan announced yesterday is faster and cheaper than trying to set up a federally funded national shelter program.

"In just four weeks," he said, "we've gotten millions of dollars worth of federal property available across the country."

Washington-based advocates for the homeless welcomed the plan, saying it was a step in the right direction. But they said the important thing is for local and federal officials to identify specifically what buildings are available so that the conversion to shelters can begin quickly.

"Actual delivery is a whole other thing, but at least it is being offered," said Tim Siegel, director of the Coalition for the Homeless, representing nonprofit groups in the Washington area.

District of Columbia officials said they could use the extra federal buildings. "We could probably find people within the city's volunteer community to operate the facilities," said Bruce Glover, a special assistant to D.C. Social Services Commissioner Audrey Rowe.

Mitch Snyder, a longtime activist on behalf of the homeless who urged use of federal buildings in congressional testimony last year, said, "it's long overdue, but it is a welcomed move . . . . realistically they've missed this winter. That's a shame for the homeless people who died." But, he said, facilities should be available next winter.