Two men found overcome by carbon monoxide in a Bethesda warehouse were listed in critical condition yesterday at the University of Maryland's shock-trauma unit in Baltimore.

The patients, identified as George Willner, 44, of Bethesda and Robert Hayes, 22, no local address, are employes of Lu Ann Co., a mattress warehouse located at 6930 Wisconsin Ave.Police said the gas fumes came from a faulty heater.

Simon Stein, the owner of the business, said Willner, his warehouse manager, complained of "feeling faint" around 7:15 Thursday night. "I told him to go home," Stein said. The Thursday shift at the warehouse normally ends at 8:30 p.m.

Authorities said the men were found yesterday morning by a passerby who noticed the mattresses had been left out overnight.Stein said he understood a neighbor saw the lights on after normal closing hours and called police.

"I don't know how they came to turn that heater on," Stein said. "It wasn't very cold yesterday and there were electric heaters they could've turned on. It's a shame. We've been in business here eight years without trouble and we're not looking for it."

The faulty heater was cleaned last fall, Stein said. "The man charged me fifty bucks. He said it was fine."