The Antitrust Division of the Justice Department has collected $6.6 million in fines from antitrust law violators since Oct. 1, John Shenefield, assistant attorney general in charge of the division, said yesterday.

"I wouldn't mind seeing the division turn into a profit center for the government," he told a Federal Bar Association luncheon.

The $6.6 million collected in fines over the past five months compares with just over $4 million collected during the entire prior fiscal year.

On reason for the increase is the effect of a law enacted in 1974 which substantially stiffened penalties for antitrust violations occuring after Dec. 21, 1974. It made them felonies rather than misdemeanors and punishable by up to three years in ajail and a fine of $100,000 for individuals. The corporate fine became $1 million.

Shenefield noted that as time goes on, more and more of the antitrust violations uncovered by the division will be subject to the increased penalties.

Another reason for the increased fines collected appears to be a greater willingness on the part of judges to sentence antitrust law breakers to jail and to impose higher fines than they had earlier been inclined to do. The Justice Department has been pushing hard for the change.