Princess Diana fainted in the California Pavilion at Expo 86 today as she and her husband, Prince Charles, were being escorted by Gov. George Deukmejian on a tour of the exhibit.

Representatives of the royal couple immediately denied that Diana was again pregnant.

The princess lay on the floor for several minutes before being helped to a back room of the pavilion. About 20 minutes later, apparently recovered, she walked out the front door to a waiting motorcade as hundreds of fair-goers cheered.

"She fell to the floor," Deukmejian told reporters afterward. "It didn't appear to me at the time that she hurt herself when she fell . . . I was obviously quite concerned."

Prince Charles resumed the tour of the pavilion, but the visit was cut short when the princess had recovered sufficiently to leave.

"Her head was down and she was helped into a rest area with Prince Charles supporting her on one side and another man on the other," said one observer.

Deukmejian said Diana collapsed as state officials were explaining the workings of a computerized bicycle design exhibit.

Prince Charles half-caught his wife as she fell, Deukmejian said, apparently preventing any serious injury.

"She moved closer to her husband and sort of tapped him on his arm and was beginning to say something to him when she fainted," Deukmejian said. "She fainted very gracefully." A doctor was immediately summoned, and reporters, who had been kept behind a cordon out of sight of the incident, were quickly hustled outside.

During her busy tour of the 170-acre Expo site, the princess was able to stop only for a 15-minute lunch.

Reporters covering the royal tour immediately began speculating that the princess was pregnant, but spokesman Vic Chapman denied it.

"No, she is not pregnant," Chapman thundered to a crowd of anxious journalists.

Diana's fainting spell occurred on one of the few sunny days on the Canadian tour. Temperatures were slightly above 70 degrees.

Chapman said the royal couple would continue with their itinerary, including a state dinner tonight, for the final two days of their week-long tour of British Columbia.

On Wednesday they were scheduled to tour a children's hospital and three more pavilions before flying to Japan for a week's tour.