The business manager of Southeastern University in the District has been fired after questions were raised about university purchasing practices, including alleged "substantial" overpayment for janitorial supplies and office furniture, the university and its attorney said yesterday.

The university's board of trustees put the business manager, John Curry, on administrative leave last week after a new auditing firm it had retained brought questionable purchasing practices to its attention in July, according to Dr. W. Robert Higgins, a university official. Yesterday the school sent Curry a letter telling him he was being fired because of "adverse publicity," Higgins said.

Curry, formerly an adjunct professor at the university until he became its business manager two years ago, is responsible for approving all the schools purchases, according to James Brent Clark, an attorney hired to investigate the matters raised by the audit. But Clark added that he does not know "what involvement Mr. Curry may have had, if any" in the overpayments found by the audit.

"The indication is that the overpricing is substantial," said Clark, who said overpayments for office maintenance materials, furniture and other goods purchased by the school may have been taking place over a period of "some months" and perhaps as long as a year.

The audit is still continuing, he said.

Curry, who lives in Potomac, said he had not been notified of his firing. He declined to comment on any allegations about his actions, pending consultation with his lawyer.

Accounts of Southeastern's overpayments were first reported Wednesday by WJLA-TV, Channel 7, which said the university's audit showed it was paying too much for janitorial supplies, books and other products, including $96 for a case of hand soap that normally costs about $36.

The television report said a major supplier of the goods were four companies owned by Gerald Schall of Middleburg, Va. Clark said he is investigating spending for a range of items, including but not limited to those in the television account.

Schall could not be reached for comment yesterday.

Last night, the station reported that Southeastern has also been spending $90,000 a year to hire security guards from a firm owned by Curry and a District police sergeant, Jack Vincent.

The action marks the second incident in which an employe of the university, a small, private business school located in Southwest Washington, has been ousted following allegations of questionable handling of university funds.

In 1981, the university fired its controller, Joyce Jobe-Balfour, who subsequently sued the school.

In depositions filed in that suit, university officials said Jobe-Balfour was fired after an audit showed that thousands of dollars in university funds had gone to a Washington cooking school of which the then-president of Southeastern was a trustee. The president, Barkev Kabarian, resigned after the audit, the depositions said.

Jobe-Balfour contended she had been fired without a hearing and that she never knew certain purchase orders were being used to finance the cooking school.

A D.C. Superior Court jury earlier this year awarded Jobe-Balfour $601,000. Southeastern is appealing the case.

Founded in 1879 by the Young Men's Christian Association, Southeastern University has an enrollment of about 1,500. It is classified as a tax-exempt education foundation but receives no federal funds except for government loans made to some of its students, according to Higgins.

The school last year dropped its athletic program and laid off some employes, after pleading financial hardship because of a declining enrollment.