Conversions of apartments to condominiums doubled between 1977 and 1978 nationally and may increase another 30 per cent this year, according to testimony yesterday at the first congressional hearing on the condominium crisis.

Nearly three-fourths of the conversions were in only seven areas - New York, Chicago, Houston, Seattle, Denver, Los Angeles and the District of Columbia, according to a statement by Philip Kozloff, president of Citicorp Real Estate and vice president of Citibank in New York.

Sen. Harrison A. Williams Jr. (D.N.J.) chaired the hearing as head of the Senate subcommittee on housing and urban affairs. Williams, calling the national condominum boom "surely the housing phenomenon of the 1970s," said it is time to ask whether Americans face a future in which the only available rental housing will be subsidized.

D.C. Mayor Marion Barry, representing both the District and the U.S. Conference of Mayors, said the number of conversions in 1978 in the District was more than five times the number in 1977. During the first three months of this year, conversions already equalled the total number in 1978. Conversions are spreading from predominantly white areas into black communities now, he said.

Barry made several recommendations about what the federal government can do to alleviate the crisis facing Washington and other cities, but noted, "The greatest role that the federal government can play is to provide more housing money for subsidized housing."

Other witnesses had more drastic recommendations. Daniel Lauber, the principal planning consultant with an Illinois-based firm, urged a national three-year moratorium on conversions unless tenants agree to them. Lauber said the level of conversions, if unabated, "will generate the worst national housing crisis since the end of World War II."

Other ideas for federal government action included allowing the federal housing agencies to give more community block grant funds to communities that develop good plans to deal with conversions. Sen. Paul Sarbanes (D-Md.), pointing out "extremely advantageous" tax benefits that encourage conversions, added, "Maybe we should think about changing tax laws to preclude those advantages."

Others, however, stressed governmental help in aiding those who want to purchase condominiums but can't afofrd them.

Testimony also was heard yesterday on a bill introduced by the two Senators from Florida that would give tenants and condominium buyers more protection through federal regulations, such as requiring developers to guarantee against defective worksmanship and to give tenants 120 days' notice of conversion.

In addition, it would provide some protection from leasing arrangements that tie rental fees for recreational facilities to increases in the consumer price index, a problem Florida officials testified has plagued thousands of condominium owners there.

Some housing industry groups vigorously oppose the bill, however. "The states are adequately addressing their individual problems" without federal regulation, the American Land Development Association contended in a statement. CAPTION: Picture, MAYOR MARION BARRY . . . seeks housing money