The Abscam bribery-conspiracy conviction of former senator Harrison A. Williams Jr. of New Jersey was upheld yesterday by a federal appeals court, which rejected claims that the FBI trapped him.

"The initial involvement of Sen. Williams with the Abscam 'sting' operation originated with the senator, not with the government," a three-judge panel of the 2nd U.S. Circuit Court of Appeals said in a unanimous opinion.

Williams, who quit the Senate last year shortly before an expulsion vote was to be taken, was sentenced on Feb. 16, 1982, to three years in prison and fined $50,000.

Because of the appeal, Williams has not begun serving his sentence.

Williams was accused of accepting a free and hidden 18 percent share of a Virginia titanium mine in return for help in finding military contracts for the venture.

In return, a fictitious Arab sheik--actually an FBI agent--was supposed to lend the project $100,000, after which Williams was to sell his shares for a $12.6 million profit.

Williams argued two points before the appeals court. He said FBI agents and operatives manipulated him into making false boasts about his influence.

Williams also argued that if a crime had been committed, he had been entrapped by FBI agents and operatives.