Two construction workers were injured yesterday, one critically, when a 60-foot crane apparently dropped a load of concrete on an unfinished parking garage, causing the structure to collapse.

The 35-ton crane overextended its arm and began to tip, said David W. Riffle, the project manager at the Shirlington Gateway office building under construction at 2800 Shirlington Rd., Alexandria. The crane operator, fearing the entire crane would fall over, dumped the concrete onto the garage's fragile timber deck, Riffle said.

Alexandria public safety officials were investigating the accident last night and would say only that it was a "crane-related accident."

Ronald W. Lease, 23, of Augusta, W.Va., was in critical condition at Alexandria Hospital with head and chest injuries. Construction workers said timber and metal bars from the garage trapped him face down on the first floor of the three-level garage.

Eduardo Arguello, 42, of 3812 Columbia Pike, Arlington, was in good condition with leg injuries at National Hospital for Orthopaedics and Rehabilitation.

"I was underneath it, but I made it out," said carpenter James P. Harrelson, 58, of Martinsburg, W.Va. "I heard timber cracking and everyone hollering 'Get out.' There was tons of weight falling."

The $15.6 million office building, due to be completed by June 1, will have an attached three-level garage, and is owned primarily by Misner/Daniels, a Fairfax development company, Riffle said. It is located between Rte. I-395 and Shirlington Road.

About 150 men were working for Eugene Simpson and Brother Inc., the general contracting firm building the 12-story office building, when the accident occurred at 3:09 p.m, police said.

"They had a hard time getting [Lease] out," said Lynn Bushnell, who was fitting the office building with new windows yesterday. "When they finally got him, they put a brace on his neck and a mask on his face. He looked pretty bad."