The administrator of Arlington County's $1 billion retirement fund resigned yesterday, after a county audit found "irregularities" in his expense reports, including trips to the Bellagio Hotel and Casino in Las Vegas and other luxury resorts.

Executive Director Bruce O. Kallos, 69, was placed on administrative leave last month after a county audit revealed improper use of the board's American Express card for travel and other expenses.

Steven D. Ivins, president of the Board of Trustees of the Arlington County Employees' Supplemental Retirement System, issued a statement yesterday after the board met to discuss Kallos's fate.

Kallos "has resigned effective immediately, and we have reached a satisfactory settlement on outstanding issues," Ivins said.

In an interview, Ivins declined to discuss the terms of the settlement and whether restitution for the estimated $10,000 in misspent funds would be paid.

"I can't disclose that. It's a personnel issue. I think that's covered by the settlement," Ivins said.

Kallos said he and the board had agreed to an "amicable parting."

"I've been there for almost nine years. We reached a resolution on all our issues," he said.

Kallos had been the fund's administrator since 1995, during which time the fund had done well, performing in the top 25 percent of public funds for the past five years, county officials said.

In recent weeks, Arlington Comptroller Barbara Liechti has been conducting an audit of the past 12 months of expenses after questions about Kallos's expense reporting surfaced this year. Records released by the county of Kallos's American Express card for the past two years show a $619.88 bill from the Bellagio and a $1,111.86 charge for the Inn at Spanish Bay in Pebble Beach, Calif.

Kallos had previously said he "screwed up" when he charged an estimated $200 on his hotel bill for an afternoon of massage and yoga at the Centre for Well-Being spa in Scottsdale, Ariz.

Brenda Kriegel, president-elect of the Arlington General Employees Network Association, had argued that the county should hire an independent investigator to conduct a five-year audit of Kallos's expenditures. She felt that the terms of Kallos's restitution should be made public to county employees.

"I'm disappointed," Kriegel said. "I do think they should have a thorough, neutral audit to get to the bottom of some of the problems that created this."