The men's International Professional Tennis Council yesterday hit controversial llie Nastase with the most severe penalty in the history of professional tennis - a three-month suspension from Grand Prix tournaments and a $5,000 fine - for his conduct in Grand Prix tournaments.

Nastase, who held the previous record for such fines ($6,000 in 1976) will not be able to play in the U.S. Open in September.

He was told of the council's decision a few minutes after he lost to Tom Okker in the quarterfinals at Wimbledon.

Nastase has been fined eight times in the last 2 1/2 years for behaviour that has included arguing with officials, players and fans. He also had made numerous obscene gestures from the stadium in tournaments.

Nastase refused to comment, but his manager, Mircea Oprea, said the council's three-month suspension could cost a player of Nastase's calibre between $50,000 and $100,000. He said Nastase's attorney would first have to read a decision before they decide whether to appeal.

I think the council could have done a year in advance, so this will ef-Oprea said. "The bookings are all done a year in advance, so this will effect several commitments."

A statement issued by the council noted it took action because of a series of breaches of the "code of conduct" by Nastase resulting in a "major" offense. The maximum penalties under the code are a fine of $10,000 and a year's suspension.

A source close to the council said the group had to act, that Nastase had simply pushed them too far.

"Too far?" asked Oprea. "I think you could say they watch him closely. Once he was fined for saying a word he did not invent and which other players use as well."