ANTWERP, Belgium (AP) _ Grandmasters Jan Timman of the Netherlands and Lajos Portisch of Hungary agreed to a draw without resuming play Sunday in the adjourned fourth game of their World Chess Championship Candidates quarterfinal.

The bishops and pawns ending had been declared a certain point splitter by ''chessperts'' when Portisch sealed his 62nd move after an exciting six- hour battle from a Ruy Lopez the day before.

But Timman, who was playing white, painstakingly analyzed the position overnight with his seconds in the hope of getting more out of the game than the half point earned by a draw.

Late Sunday morning, he called up his opponent in the Antwerp hotel, where the match is being played, to propose signing the peace.

Portisch, now leading 2 1/2 -1 1/2 in the six-game, knock-out match, accepted and informed Yugoslav referee Svetozar Gligoric of the outcome.

The draw meant a serious setback for the 37-year-old Timman, who desperately needed a victory to catch up with the 51-year-old Hungarian.

With only two more games to go in the match, his chances of gaining a berth in the semifinals seemed slim.

A win in Monday's fifth game, in which Timman will be playing with black, was considered unlikely by the experts following the Antwerp duel.

''Portisch will be satisfied with a draw,'' explained Dutch grandmaster Genna Sosonko, ''and he's such an able defender that Timman would be taking a great risk indeed if he tries to win with black. The match might be over at once.''

According to Sosonko, Timman will wait for the sixth game, scheduled for Wednesday, to try and tie the score.

If he then manages a win with white, the match will be extended with two more games, to be followed by sudden-death rapid contests if the tie persists.

The Antwerp match is one of a series to select a challenger who will play world champion Gary Kasparov for his title in 1990.

On Saturday, Arthur Yusupov of the Soviet Union defeated Canada's Kevin Spraggett in their first rapid game in Quebec to reach the semifinals, while former Soviet world champion Anatoly Karpov was well on his way to a victory over Johann Hjartarson of Iceland in their quarterfinal contest in Seattle.

Jonathan Speelman qualified for the semifinals by defeating fellow British grandmaster Nigel Short in August.