San Francisco Supervisor Robert Mendelsohn was questioned closely about the campaign debts yesterday by the Senate Energy and Natural Resources Committee. But his confirmation as assistant secretary of the interior for policy, budget and administration seemed assured.

Mendelsohn had $150,000 in campaign debts and outstanding loans mainly after losing races for California state controller in 1974 and the state senate in 1976.

Since he was nominated in February for the Interior Post, all but $68,000 has been forgiven or repaid, he told the committee. The remainder is being refinanced by remortgaging his San Francisco home, he said.

Mendelsohn's nomination came under close scrutiny by the White House after a series of articles in the San Francisco Bay Guardian, a weekly newspaper with a circulation of 27,000 accused him of "conflicting statements" about his campaign contributions.

In a letter to the Senate committe, Guardian publisher Bruce B, Brugmann said Mendelsohn should not be confirmed because, as a member of regional and state coastal commissions, he has "consistenly voted on behalf of his major campaign contributors."

Mendelsohn denied the charge and said he has sought a "middle road" between developers and environmentalists on the commissions.

Senators at the hearing yesterday said they were satisfied with Mendelsohn's financial arrngements, which were cheeked by White House counsel Robert Lipshutz and Interior Solicitor Leo M. Krulitz.

The bulk of Mendelsohn's campaign debts were forgiven at an April 22 fund-raising dinner in San Francisco. Severl contributions were returned to avoid appearance of conflict of interest with companies or individuals that might do business with the Interior Department.

Interior Secretary Cecil D. Andrus praised Mendelsohn as "a person of the highest ability, dedication and energy." As a $50,000 per year assistant secretary, he would review policy and budget matters, environmental impact statements, internal organization, procurement and various investigations.