A teen-age boy was in critical condition early today after being bitten by a poisonous snake in an incident police said they believed was connected with a break-in last night at the reptile house of the National Zoo.

While the youth, who was not identified, was undergoing emergency treatment at Children's Hospital early this morning, police were investigating both the snake bite and the break-in, in which two snakes were taken.

A zoo police sergeant was unable to say immediately what kind of snakes were taken in the break-in, but one source reported that at least one was a poisonous African viper.

D.C. and Metro police said that the youth who was bitten was carrying a bag over his shoulder when he alighted from a Metrobus at 15th and K streets NW about 11:30 p.m. last night. The bus was identified as a southbound L-2 that had earlier passed the zoo.

After stepping from the bus, the youth quickly returned, telling the driver he had been bitten. The driver then notified authorities and an ambulance was dispatched for the youth.

"The snake that apparently bit him was very poisonous," said 2nd District police Capt. Rodney Murray. Children's Hospital officials said attempts were being made early today to locate antivenin serum with which to treat the youth.

Capt. Murray said no details were immediately available on either the bite or the break-in, which was reported to D.C. Police about 12:30 a.m. But, he said, "it would stand to reason that there's some connection."