Rep. Parren J. Mitchell (D-Md.), the original sponsor of legislation guaranteeing minority contractors a share of $4 billion in annual public works spending, said yesterday he was seeking the support of civil rights groups to defend the program before the Supreme Court.

At a news conference called during Congress' summer recess, Mitchell said minority contractors will suffer enormous damage if the high court finds the program unconstitutional.

New York contractor H. Earl Fullilove and the General Contractors Association of New York, Inc. contend that the program unconstitutionally discriminates against them.

"The provision...which imposes disadvantages upon persons who bear no responsibility for whatever harm the beneficiaries...are thought to have suffered, cannot be justified," the New York contractors argued in a brief filed with the Supreme Court Tuesday.

The constitutionality or the program has been upheld by lower federal courts in New York and 25 other states, according to Mitchell's legislative counsel. Federal courts in Montana and Vermont, however, have ruled it unconstitutiona, and a California challenge is pending.

Mitchell said yesterday that the program, approved by Congress in 1977, has given black, Spanish-speaking, Oriental and native American contractors "an expectancy of some $400 million in contracting opportunitites."

He also noted that he has talked with a variety of groups - including the National Association of Black Manufacturers, the Association of Minority Contractors and the Urban League - and urged them to file friend-of-the-court briefs in support of the program.

A spokesman for the American Civil Liberties Union said the ACLU already is planning to draft a brief in support of the program.

In addition to the federal program, which is administered by the Economic Development Administration and guarantees minority businesses 10 percent of the federal public works contracts, a number of states and municipalities have adopted similar plans.

Under a 1976 ordinance, 25 percent of all District of Columbia construction and service contracts must go to minority-owned businesses. The Maryland General Assembly enacted a 10-percent setaside program in 1978. The state of Virginia has no such program.

Mitchell defended the program against charges that white contractors have defrauded it by establishing businesses with minority "front" owners to obtain setaside contracts. "The vast majority of the money went to true minority firms," and fraudulent firms received no more than 3 or 4 percent of setaside funds, the congressman said.