ST. LOUIS (AP) _ A woman convicted of stealing money from the law firm of a man who recently withdrew as the nominee for deputy U.S. attorney general was sentenced Friday to 18 months in prison and fined $5,500.

Denise Sinner had claimed during her trial that John C. Shepherd, a partner in the law firm who was nominated to be the No. 2 man in the Justice Department, had authorized her to write checks to herself because they were having an affair.

Shepherd denied the accusations under oath, and Sinner never presented any evidence to show that there had been an affair.

Sinner, 29, of St. Peters, was sentenced to 12 months in prison and fined $5,000 for stealing $147,000 from Shepherd, Sandberg & Phoenix while she worked as a bookkeeper for the firm for several months beginning mid-1986. She was alleged to have used the money for personal expenses and to purchase luxury items such as a BMW.

Sinner was sentenced to an additional six months and fined $500 for making a false statement to the government. The prosecutor said she had falsely claimed in a doctor's letter to have terminal cancer.

Sinner's attorney said the convictions would be appealed. She is free on $10,000 bond.

On April 5, Attorney General Edwin Meese chose Shepherd to become the No. 2 man in the Justice Department in the wake of the March 29 resignation of Arnold Burns.

But two weeks later, Shepherd withdrew from consideration for the job, citing the public scrutiny he was undergoing and the pressure it was putting on his family.