A former government supplier who allegedly swindled the General Services Administration out of more than half a million dollars through three separate fraud schemes was sentenced here today to six years in prison.

The sentence for businessman Matthew Smith, 54, of Washington, is the harshest meted out so far in the investigation of bribery and corruption in the GSA. Sixty-seven persons have been convicted and sentenced so far.

U.S. District Court Judge James R. Miller told Smith today that if he assigned him "a place on the scale of all these defrauders," Smith would rank "at the top of the heap."

Smith, the owner of three office supply firms in the Baltimore-Washington area, was indicted for two fraud schemes last March. He refused to cooperate with the government's investigation of corruption in the GSA, but pleaded guilty to two counts of filing false claims last July.

The two counts charged Smith with billing the government for thousands of pen refills that the GSA never received. Altogether, Smith billed the government for $777,962 for supplies he purchased for $221,169, according to prosecutor Elizabeth H. Trimble.

The second indictment, which charged Smith with defrauding the U.S. through a bribery scheme with another firm, James Hilles Associates, Inc., and two GSA store managers, was dismissed at the sentencing today. Trimble said Smith and the managers split $138,000 from that alleged bribery and fraud scheme.

In addition, Smith was named last month as an unindicted co-conspirator in a third scheme. That indictment charged that Smith and others stole goods from the GSA stores and fenced them in New York. Three persons are scheduled for trail in that case in January.

Nationally, 73 people have been indicted so far in the GSA bribery scandal. Of those, 62 have pleaded guilty, five have been convicted after trails, and one had been acquitted after a trail. Five people are still scheduled for trials.

Smith started his three office supply companies after he retired for health reasons as a financial analyst with the Navy in 1976.