The Small Business Administration today will lift its 3 1/2-month-old moratorium on the federal government's main program of assistance for businesses run by blacks and other disadvantaged persons.

The ending of the moratorium means that eligible firms not now in the program can apply to join the 1,485 companies qualified to bid on the contracts SBA sets aside for businesses owned by socially and economically disadvantaged people.

The moratorium was put in effect on July 20, immediately upon the conclusion of a series of hearings on the program held by Sen. Lawton Chiles (D-Fla.).

Chiles' hearings unearthed a series of alleged abuses, most of them several years old, ranging from participation by affluent members of minority groups to instances of blacks fronting for white businessmen seeking to take advantage of the so-called 8 (a) program.

In a prepared statement, SBA administrator A. Vernon Weaver said yesterday, "I am confident that we have identified the irregularities that affect the program, and are taking appropriate actions."

Only three weeks ago, on Oct. 19, Weaver told a House small business subcommittee the moratorium would continue in effect at least until January, two months later than he had estimated earlier.

Weaver was sharply criticized by the subcommittee for the delay in reopening the program. In 1976 SBA awarded about $370 million of 8(a) contracts to disadvantaged businesses, which included about 80 per cent of all federal purchases from minority businesses that year.

SBA's deputy chief of the 8(a) program, Ed. Lewis, said yesterday Weaver "did not have the information he has now" when he told the committee the program would continue to be frozen until January.

"We have reviewed a number of the firms that are questionable," said Lewis. "We have a handle on the program now."

During the moratorium, no new entrants were permitted to 8(a), although companies already in the program continued to receive contracts.

Lewis said a large number of the firms in 8(a) were reviewed during the moratorium. Of them, 52 were dropped, some because SBA did not feel they were eligible, others for failure to comply with some administrative aspects of the program.

Weaver also set up a review committee to look at most aspects of the 8(a) effort, and recommend changes. He said yesterday the committee is still studying the program.

"I regret any inconvieniences or hardship the restrictions may have had on firms which were seeking entry into the program," he said. "I want to re-emphasize my commitment to the program, and my pledge to strengthen it, and make it more viable and meaningful for the socially and economically disadvantaged firms it is specificially designed to benefit."