University of the District of Columbia President Robert L. Green and his wife used the university's tax exemption to avoid paying sales tax on more than $2,000 of personal items purchased at several area department stores, according to a report released yesterday by D.C. Auditor Otis H. Troupe.

Troupe's report said Green and his wife, Lettie, had used the school's tax exemption to make purchases totaling $2,475.30 at Saks Fifth Avenue, Neiman-Marcus, Garfinckel's and one other business between last September and March. They should have paid 6 percent more, or $147.50, in sales tax on these items, the report stated. The report, which did not specify what items were purchased, said that using the school's tax exemption for personal purchases violates District law and university policy.

Troupe, who met with Green last week, said in the report that the president and his wife "indicated that neither of them were in any way aware" that the tax exemption should not be used for personal items.

"Dr. Green has offered to make full restitution of all wrongly exempted taxes," Troupe said in the report.

Officials at the publicly financed university said yesterday they could not comment on the report until they had seen it.

The report is part of a wider investigation by the auditor of expenditures of university funds by the Greens. No other findings have been released.

The Washington Post, using documents obtained under the D.C. Freedom of Information Act, reported last month that since he took office in September 1983 Green, 52, had billed the university for trips to two funerals and a wedding and charged UDC for a $260-a-night hotel room in Atlanta.

Records obtained by the Post under FOIA also showed that Green had spent $83,200 on catering in a 21-month period and had charged nearly $18,000 worth of small household items to the university.

In his report, Troupe said the Greens may have used the tax exemption for more transactions than those uncovered in the audit. "Similar transactions may have also occurred through credit card or check purchases" that the auditor was unable to review, the report said. Green has said he will review his own records to determine whether he or his wife made other purchases using the tax exemption.

To use the tax exemption, a university employe must sign a form before getting a tax exemption certificate that, when shown to a vendor, exempts the employe from paying sales tax. Employes also are expected to submit vouchers for their purchases.

"An explanation has not been provided concerning how the president and his wife gained access to tax exemption certificates," the report said.

"While the taxes due on the purchases . . . may be viewed as minimal, they nonetheless reflect an impaired system of checks and balances and ineffective controls," Troupe said in the report. He said the unauthorized use of the exemption has resulted in "the loss of sales tax revenues to the District government" and "jeopardizes the university's tax exempt status."

Troupe recommended establishing guidelines limiting access to the certificates and suggested Green repay the taxes.