King Hassan of Morocco has surprised U.S. officials by canceling an official visit to Washington scheduled for next week "because of fatigue stemming from his recent heavy workload," the State Department announced yesterday.

Department spokesman Bernard Kalb said Moroccan officials had explained that Hassan's doctors have advised him not to travel. However, the king's unexpected action caused speculation in diplomatic circles about whether he might have had some other reason for not wanting to visit here at this time.

Other State Department officials, who asked not to be identified, said they did not know whether Hassan's health was the real reason for canceling the visit. But they noted that in the past, the king has canceled planned trips to this country on short notice.

Some officials speculated that Hassan might have decided not to come because he was aware that he would be subjected to American criticism over his announced plans for a union between Morocco and Libya. The administration, while regarding Hassan as one of America's principal Arab allies, has been very critical of the king's pursuit of close ties with Libyan leader Moammar Gadhafi, whom the United States considers a major supporter of international terrorism.

The officials said U.S. concern has abated somewhat in recent weeks because virtually no progress has been made toward an actual union of Libya and Morocco. Still, as one official said, "The king knows that he would be reminded of U.S. disapproval at the highest levels here, and it might be that he just didn't want to hear it."

The officials discounted rumors that Hassan might have been angered because his trip would have been treated as an "official visit" rather than a "state visit," which involves greater ceremonial honors. They said that Moroccan officials had been aware for some time that Hassan had been invited for an "official visit" and had not expressed any objections.