Human error, carelessness and bookkeeping problems in some of the General Services Administration's leasing divisions may cost the government as much as $43 million over the next 10 years, the General Accounting Office reported.

The GAO spot-checked leases in four regions. It found seven instances in which the GSA had failed to move quickly enough to get a lease for office space extended at a low-cost rental rate. The report said that there were six other renewal options, including five in Washington, that would have been missed if GAO auditors had not spotted them.

The auditors said that GSA officials "have taken steps to minimize the recurrence of the missing lease-renewal options . . . . However, the management of lease-renewal data continues to be a problem."

The computer the GSA uses to track leases is considered antiquated by some GSA officials, and a new system won't be in operation for at least a year. In the meantime, GSA officials are supposed to keep track of the most complicated leases by hand.

The largest mistake, which could cost the government between $24 million and $33 million, was discovered in September in the San Francisco regional office. It prompted former representative John L. Burton (D-Calif.) to ask for the GAO report.

The GSA subsequently fired the two supervisors it held responsible for that error as well as real estate division director Joseph Yiakis and leasing branch chief Kathleen Kennedy.

GAO auditors found a total of 109 errors in that region's file of 654 leases.

The most significant new case involves the Landow Building in Bethesda, where the GAO said the government will lose between $6 million and $9 million over the next 10 years. There was, GAO said, "Conflicting information in the lease file pertaining to the number of days required before lease expiration for issuing renewal notice to lessor."

"We have re-reviewed the inventory of leases three times since the issue first arose," said James G. Whitlock, the GSA's public buildings commissioner for the Washington region. "We regard this as a very serious matter."