State Department and Mexican officials said yesterday that they have found no trace of a top U.S. Energy Department official who disappeared nearly three weeks ago in an apparent boating accident off the eastern coast of Mexico.

Barton Isenberg, 34, assistant administrator of DOE for enforcement, disappeared March 23 while boating with a childhood friend, Ronald Shore, an Aspen, Colo., businessman.

State and Energy department officials said yesterday that there is no evidence of foul play in the accident off the coast of tropical Cozumel Island. However, Steve Dickstein, Isenberg's cousin and spokesman for the family, said the family has retained a private investigator from New York to look into the incident. He said the two men were vacationing there and training to be certified as skin divers.

Dickstein said both men's families were upset that they were never notified by the State Department of the accident and that a family member first learned about it from a travel agent eight days after it occurred.

"The fact that there are so many contradictions [in explaining the accident and rescue efforts] that have been offered to date, is terribly disquieting to everybody," Dickstein said.

"If in fact the State Department knew of the accident on March 23, and did not contact the family, I can only indict them for a glaring insensivity, but I cannot conclude that they had any sinister motive," Dickstein said.

At DOE, Isenberg headed the division responsible for enforcing pricing regulations at most retail gasoline stations and pricing and distribution regulations for some crude oil refineries.

After they heard from the travel agent, worried family members notified some of Isenberg's close and influential friends here -- journalists, lawyers and in the White House -- who began gathering information through their own network, only to find it at times confusing and contradictory.

What eventually emerged from Mexican authorities was the story that two men, Manuel Wicad and Carlos Erique Gonzales, saw Isenberg and Shore's catamaran sailboat overturn off Cozumael in shark-infested waters. According to Cozumel port Capt. Humberto Camargo, Wicad and Gonzales attempted to rescue the men in a speedboat, but ran out of gasoline.

Camargo said the two Mexicans paddled to shore, refueled and went back to attempt a rescue, but found nothing as night fell. The next day, he said, Mexican authorities began a search through the area.

"We found nothing, not the boat, not them," Camargo said yesterday in Cozumel. "They have completely disappeared. It's curious, very mysterious."

Dickstein and several of Isenberg's friends said they couldn't understand the lack of information about the incident and the fact that the catamaran never turned up.

According to relatives and others, the catamaran was made of fiberglass and presumably unsinkable. In addition, both men were good swimmers and Isenberg had taught sailing and swimming at a youth camp in the Bahamas during his college years.

"There was never any indication from talks with the State Department that they were aware of the disappearance as early as March 23," Dickstein said. "I had the distinct impression that they did not know about this, and the Mexican government had been lax about notifying the families and the American government."

"Monday, March 31, was the first time that I had heard anything about the accident," said Penny Miller, a friend of Isenberg and a special assistant to Vice President Mondale. "Monday night I called people in the embassy in Mexico, and the people I talked to didn't seem to know anything about it.

"I called, trying to seek permission of the Mexican government to bring in the U.S. Coast Guard in an inoffensive way so that they could be of assistance [to the Mexican government] during search and rescue efforts," Miller said.

Miller said she and Douglas Huron, an attorney in the White House counsel's office, met with former ambassador Esteban Torres, special assistant to President Carter for Hispanic affairs.

"Ambassador Torres was of some help talking to the Mexican officials the next day [April 1]," Miller said. "Every report I've gotten indicated that the Mexican government was very thorough and helpful during the search."

Vernan McAninch, U.S. consul general in Mexico, said the embassy in Mexico knew nothing about the incident until Miller's call March 31.

However, McAnich said further checking revealed that consular officials in Merida in the Yucatan peninsula said they were notified March 24 about two missing Americans, but had little information other than names.

"It's easier for us to contact you in Washington than for us to contact the consul in Cozumel because of lack of communications in the tropical Yucatan," McAninch said. "We always make an attempt to notify the kin of missing persons. But by the time we had the information and called the Conzumel Rescue Service, they told our officials that the two Americans had been rescued March 26 and were in good condition.

"It was a false report," McAninch said, "and we didn't learn that until April 1. We protested our not having been told that the report had been false sooner."

Isenberg, who had served previously as deputy attorney general of Pennsylvania, was described as warm, gregarious and well liked by his friends and coworkers. Friends said he loved their children and would take them for frequent outings.

"He was extremely dedicated," said Kenneth Adams, a lawyer friend, who added that Isenberg was often bothered by "the frustrations of trying to make a large government program work effectively."