The two occupants of the light plane involved in the near-collision with President Reagan's helicopter Thursday did not realize that they had flown over Reagan's California ranch and passed his airborne entourage until after they landed in Orange County, the passenger said in an interview published yesterday.

Harlan Lee Jones, the passenger in the single-engine Piper Archer, told The Orange County Register that he was en route to a business meeting with Donald Nixon Jr., nephew of former president Richard M. Nixon, when he and pilot Ralph William Myers became lost over the mountains northwest of Santa Barbara.

Myers, an Army private who was absent without leave from his post at Fort Lewis, Wash., remained in military custody yesterday in Los Angeles. He will be returned to the Fort Lewis base Monday or Tuesday to face possible disciplinary action for his absence, base spokesman Bob Rosenburgh said.

The 32-year-old private could also be cited with "conduct unbecoming a soldier," Rosenburgh said.

In Los Angeles, a spokeswoman for the U.S. attorney's office said the government is considering filing civil or criminal charges against Myers.

According to the California paper, Jones said he and Myers were confused when their plane entered restricted airspace and passed within several hundred feet of the helicopter carrying the president to his mountaintop ranch.

Myers was searching the plane's cabin for his contact lenses and Jones, who is not a pilot, was trying to navigate the craft about 500 feet above a ridge when two military helicopters loomed into view, Jones said.

"We dropped down in altitude closer to the mountain away from their path. They passed way off to the right," Jones told The Register. "There was no near-miss," he added.

The pilot of the president's helicopter, Marine One, later said he gently banked away from the Piper, and members of the president's entourage said they were unaware a near-collision had occurred.

According to a transcript released by the Federal Aviation Administration, the following radio exchange took place between air traffic control in Santa Barbara and Marine One:

CONTROLLER: "Marine One, traffic 12 o'clock, two miles, opposite direction, altitude unknown."

MARINE ONE: "Marine One, we're looking. {Pause.} Yeah, Marine One, we've got this guy right underneath us. He just flew over the ranch at about a hundred feet. I want him violated, if we can find out who it is."

Jones said he did not understand why a helicopter, Nighthawk Three, pursued. "I thought the guy was crazy," he said.

Nixon met Jones at John Wayne Airport, about 120 miles south of Reagan's ranch, shortly before Secret Service agents arrived on the scene, according to a dispatcher at the aviation company that serviced the plane. Nixon and Jones work for Tower Financial Corp., a New York firm that provides corporate financing, The Register reported.

Jones, 53, of Lake Oswego, Ore., said he had hired Myers to fly him from Vancouver for the business meeting. He said Myers told him he had obtained a six-day leave for the trip, The Register reported.