A former administrative assistant to Rep. Daniel J. Flood (D-Pa.) received $25,000 in cash from a New Jersey businessman in exchange for helping obtain government contracts for a vocational school in Wilkes-Barre, Pa., in 1972, according to a Justice Department memoradum made public in Los Angeles.

The allegations were filed at the start of an unrelated bribery trial in which the former Flood aide, Stephen Elko, and an associate. Patricia Brislin, were convicted two weeks ago in U.S. District Court in Los Angeles.

According to the Justice memo. New Jersey businessman George Young, developer of a computerized training device for vocational schools, said he gave $25,000 in cash "campaign contributions" to Elko in the Bahamas and watched the congressional aide and Britain "secreted the cash in money belts in order to bring it back to the U.S."

The cash was given in exchange for help in securing vocational school financing from the departments of Labor and Health. Education and Welfare, the memo alleged. Flood is chairman of the House Appropriations subcommittee for those departments.

A spokesman for Flood said yesterday that the Pennsylvania congressman "does not even know George Young," and said a search of the campaign records turned up no indication of such a contribution.

Elko, who left Flood's staff in June, 1976, and Brislin were convicted two weeks ago in federal court in Los Angeles on charges of soliciting and receiving approximately $25,000 in bribes in exchange for using the influence in Flood's office to obtain accreditation for federally funded trade schools on the West Coast. They have tot been sentenced.