MBTA OFFICIALS made the case on Monday for privatizing the agency’s warehouse and parts operations even as they continued to investigate what appears to be a major loss of money at parking lots managed by a private vendor who may be on the way out.

Brian Shortsleeve, the T’s chief administrator, said the agency is continuing to investigate discrepancies between receipts and actual cars parked at various MBTA lots. The T initially asked its parking lot operator, LAZ Parking Ltd., to investigate, but then brought in the transit police and a private auditor when the probe took a more serious turn.

The T initially said the parking revenue discrepancies were confined to the North Quincy Station parking lot. They subsequently said there were also problems at Lechmere and Riverside, but then withdrew Riverside after it was determined there was no revenue loss there.

MBTA officials have been tight-lipped about the size of the problem, but revenues at many of the T’s parking lots jumped dramatically in March and April after the discrepancies first surfaced and two LAZ employees were fired. The revenue jumps at several lots, including Riverside, suggest the loss of parking revenue may be bigger and more widespread than earlier believed. T officials are now refusing to release any other parking revenue numbers until the investigation is completed.

Shortsleeve recently put a new management structure in place to oversee the T’s parking operations and is reaching out to parking lot operators for information on improvements that could be made. He said the agency will then solicit proposals from parking lot operators; Shortsleeve declined to say if LAZ is on the way out, but that appeared to be a clear possibility.

“A request for information is out,” he said. “The next stage will be request for proposals to test the market for partners that can help us drive our parking business, both in terms of the revenue levels as well as the operations.”