There's an Asian cobra on the loose in Silver Spring.

Or maybe not Silver Spring -- the poisonous two-foot snake may have slithered out of town by now, because it isn't clear how long ago it escaped.

A cobra? Well, maybe it's a cobra. Maybe it isn't. Only its owner knows for sure. Like his snake, Kevin Wisneski, formerly of 1108 Dryden St., was nowhere to be found yesterday.

Dryden Street is a shaded little avenue of modest homes near Sligo Creek. Neighbors said Wisneski, when he was evicted in July from his rented basement, left behind two caged snakes. That much seems clear.

Lt. Richard Swain of the Montgomery County police said a new occupant of the home, Jack Johnson, called the Silver Spring station Thursday to say that he had noticed that one of the snakes was missing.

"It still remains unclear when it escaped," Swain said yesterday.

Word of a cobra on the loose spread in the neighborhood late last week, but whatever fear it may have generated seems to have subsided.

"I really don't think there's anything to worry about," said Joseph DiBella, who lives across the street. "He's gone by now."

"It probably went down the sewer," said his wife Joan. "Probably ended up down the creek or something."

Others figured that it headed for the underbrush of nearby Sligo Creek Park.

"I think it's long gone now," said Karen Contrell, another neighbor. "There are other hazards to worry about. We had some raccoons around here before, and we didn't know if they were rabid or not."

Still, she decided not to lie out in the sun during the weekend, and some of her neighbors tread lightly in their gardens.

Police said they do not know where Wisneski lives but said that he called them Friday after learning that they had some questions about his pets. They said he identified the missing snake as a poisonous "monocled cobra" and the one still at the house as a poisonous "African bush snake."

"African bush snake -- there ain't no such thing, in plain English," said Laurie Bingaman, a reptile specialist at the National Zoo, where the snake was taken. She identified it as a harmless stripe-tailed rat snake, found in parts of Asia. So was the "monocled cobra" really that?

"Who knows?" Bingaman said. "But I think the safest thing to do is assume that it does exist." Wisneski described it to police as dark brown with a diamond mark behind its head, and 2 to 2 1/2 feet long.

That would make it almost full grown, Bingaman said. What does one do if one sees it? "Turn around," she warned, "and walk away slowly." Then call the county's animal control department at 279-7525.