The Exxon four blocks from the Capitol is a one-aisle, full-service gas station where lawmakers roll up, have their windshields wiped, their petrol pumped and after enough chatty pit stops, join the wall of autographed portraits.

So it seemed peculiar Tuesday night when eager attendants were waved away by two new customers in a blue van who insisted on pumping the gas themselves, refusing to let anyone near the vehicle.

Because the two men also appeared to be Middle Eastern, millennial hysteria is in the air and police relate all kinds of stories about terrorists, the manager of that gas station said his tip to the police that night was cautious vigilance.

The FBI heeded the call and, with D.C. police, put out an alert for the 1989 Mitsubishi van with Texas plates.

The woman who sold the van to the men just outside Dallas was called and questioned, although FBI officials won't say what she said. In the District, at least one motorist driving a similar van was pulled over and questioned, police said.

The van has yet to be located, and a potential threat has been neither confirmed nor denied by FBI investigators. Still, the call was a valid concern, FBI officials said, adding that the coming new year has heightened awareness of anything suspicious.

"The millennium celebration is a couple of days away, and we are just trying to be vigilant if a citizen reports something suspicious," said FBI spokesman Greg Horner.

What makes FBI officials most interested in the mysterious van is that the occupants told gasoline attendants of the full-service station to keep away. "They didn't want the gas station attendant around the van. That could mean any number of things," Horner said.

"I'm just especially alert because of all the things I hear," said the manager, who was chagrined at the attention his call received and asked not to be identified. "I just called it in to be sure, to be careful."

Others called his actions a witch hunt.

"Vigilance against possible threats is reasonable, stereotyping is not," said Hussein Ibish, communications director for the American Arab Anti-Discrimination League. "What was the illegal activity here: fueling while Arab?"

The National Capitol Response Team, with the FBI, responds to calls on about three to six threats or suspicious packages a day in the District, Horner said. "It is not unusual that we track these kind of situations," he said.

Perhaps, law enforcement officials feel embattled for not being vigilant enough, Ibish said, speculating that "they would rather hear from me than, God forbid, have something terrible happen."

That kind of overcorrection would be almost tolerable, he said, were it not for the apparent singling out of the men for their appearance.

"Let's say the same guy calls police and says 'There are two men gassing up here, and they look foreign. They look Vietnamese. Maybe they're from Southeast Asia.' You would not see the same reaction you saw today."

But Horner characterized the call to authorities as legitimate. "It's awareness, not paranoia," he said.