A report on a special investigation of the county's finance office sharply contradicts Howard County Executive J. Hugh Nichol's explanation for the loss of $283,280 in alleged embezzlement schemes by office employes, the County Council's internal auditor said today.

Auditor Jeanne A. Johnson, citing the findings of the accounting firm of Peat, Marwick Mitchell & Co., blamed the alleged thefts on "weak management controls" and "very passive" supervision in the office.

Nichols had blamed the losses on "collusion" among office employes that enabled them to circumvent what he said were adequate management controls. He had also absolved finance director J. Darrell Campbell of direct responsibility for the thefts and expressed confidence in his abilities.

But the report, released last week, concluded that finance office controls were "extremely weak" and "ineffectual," the design of the automated personal property tax system "poor," and the administration's response to earlier auditor's warnings inadequate.

Two former cashiers in the finance office face trial on theft charges in connection with the loss of $277,280 from county coffers between November 1979 and January 1984. The alleged scheme, as outlined in the report, involved the cashing of property tax checks and the altering of tax accounts to hide the missing amounts.

A third former cashier has been charged in an unrelated scheme with the theft of $6,000, part of an additional $26,300 in losses that the latest report attributes to "financial irregularities."

"Collusion was not the name of the game," Johnson said. "That explanation doesn't apply to this situation at all."

Johnson's characterization of the report, in an interview, followed a news conference in which she, Council Chairman Elizabeth Bobo and a partner in the accounting firm discussed the investigation in detail.

Bobo said she was not familiar enough with Campbell's background to call for his resignation, noting that department heads, who are political appointees, are not confirmed by the council prior to their appointment.

"Obviously, these are not the management practices I'd like to see in county government," she added. "The report makes it pretty clear that the thefts could have taken place without collusion."

Nichols did not return a reporter's telephone calls.

"We are going to look at the report," said Campbell. "If there is any implementation needed we'll take the necessary steps."