Interior Secretary James G. Watt is pondering his future this weekend while staying at the California ranch of a wealthy young developer who served as one of Watt's aides for a few months early this year.

Watt is visiting the ranch of Thomas J. Barrack Jr., near President Reagan's in the mountains north of Santa Barbara. Barrack served as a deputy undersecretary of interior for the first three months of this year. Then he moved to the Commerce Department, where he was expected to be nominated as assistant secretary for trade development and to head an interagency task force on coal exports. But in June he left the government abruptly to return to California.

White House personnel officer Joseph Ryan said yesterday that he recalled that Barrack was recommended for an administration job last fall by E. Pendleton James, who headed the personnel office and knew Barrack from California.

After a round of interviews with Cabinet officials, Ryan recalled, it was decided that Barrack would go to the Commerce Department. But there were no openings there at the time, so Barrack joined Watt. Ryan added that Barrack left Washington because he got a good offer to return to private business.

Barrack's financial disclosure statement shows that he was a business associate of the California construction company owner who bought the house of White House counselor Edwin Meese III last year.

When Barrack joined Watt's staff a press release described him as a "successful California businessman, lawyer, livestock raiser." It quoted Watt as saying that Barrack's experience would "strengthen our management team at Interior so that we can continue to improve stewardship of the resources entrusted to our agencies." An Interior Department spokesman said recently that Barrack traveled often with Watt, but had no defined duties.

A source familiar with Barrack's work at the Interior Department said he worked on "policy outreach" and "with the interest groups." Barrack gave Watt "sensible, realistic advice on how the world was working," the source said. "If Jim Watt had more aides like Tom Barrack, he'd be in a lot better shape."

Barrack's financial disclosure statement shows that he received more than $750,000 last year from a series of real estate transactions and from his job as senior vice president of the West Coast division of Oxford Properties Inc., a Canadian real estate development firm.

The statement also shows that in 1982 Barrack had assets of at least $3.5 million and debts of more than $2.8 million. During the year he paid off many of the debts and owed less than $1 million by January, 1983.

One of Barrack's liabilities was a note for more than $250,000 to Howco Construction Co. of Santa Ynez, Calif., which was paid off in January. Howco is headed by Irv Howard, who bought Meese's house in San Diego in August, 1982, for $307,500 after it had been on the market for 20 months.

Howard worked with Barrack at Oxford Properties and lived near him in Santa Ynez. Howard did not move into the Meese house, and sold it in June at a loss of $32,500. Sources familiar with the transaction said Howard handled the sale through Ted Elkin, another associate of Barrack.

Howard said in a recent interview that he might have heard that Meese's house was for sale from Barrack. Barrack couldn't be reached for comment. Meese declined to answer questions on whether Barrack had introduced him to Howard.