Two Washington teen-agers on their way to lunch this week spotted a strange object lying in Wisconsin Avenue near Tenley Circle: a lead-encased vial that turned out to be filled with radioactive material.

The youths, Peter Hutchins, 17, and Judson Berry, 15, picked up their find and took it with them to a nearby bank and then to the McDonald's at the Mazza Gallerie before eventually carrying it back to Wilson High School, said Hutchins yesterday. There they dumped it in a locker and went to classes before showing it to officials.

It wasn't until they made a collect telephone call to the Massachusetts firm that manufactured the substance, Hutchins said, that they determined it was an isotope used in medical research and should not have been handled.

Although the level of radioactivity was small and the students were unharmed in their Tuesday adventure, the incident has sparked an investigation by officials of the Nuclear Regulatory Commission and the National Institutes of Health who want to know how the vial got into the street in the first place.

"There is some circumstantial evidence that [the vial] was part of a shipment that was on its way to a Department of the Army research center at Fort Detrick, Md.," said Karl Abraham, a regional spokesman for the NRC. "The shipment came from Massachusetts by truck to the parking lot of a company called Pharmatopes."

Yesterday, Ray Taukulis, manager of Pharmatopes Inc. at 4545 42nd St. NW, said that his firm receives shipments from the trucking company, but is not licensed to receive the isotope that was found. Abraham said that Pharmatopes was not involved in the incident.

Pharmatopes, located a block off Wisconsin not far from Tenley Circle, is Washington's only seller of radiopharmaceuticals to area hospitals. The company deals with products that are used in the diagnosis of medical disorders such as tumors and cancers, said Taukulis. It distributes radiopharmaceuticals such as galium and technetium that are used to help pinpoint tumors in the body.

Pharmatopes receives products each night about 1 or 2 a.m., Taukulis said, and vehicles carrying deliveries for both Pharmatopes and other destinations sometimes transfer cargo to another local truck while stopped at Pharmatopes.

"When they the trucking company do a mix transfer, it is done in front of our building and not in the parking lot," said Taukulis, adding that his company does not control use of the parking lot.

"This isn't something that happens in the normal course of events," said Michael E. Durso, Woodrow Wilson principal. "You can't help but wonder if this has happened before. Suppose it was a younger child who found it?"

"Finding that thing was kind of like a movie or a dream. We didn't realize it was dangerous at first," said Hutchins, a junior at Woodrow Wilson. "My main concern is that it should never have been on the street. It would have been much more serious if we had touched the liquid."

The vial, encased in a lead case known as a "pig," contained chromium 51, a radioactive isotope that is used in red blood cell research, Abraham said. A label identified it as the property of the New England Nuclear Corp. in Billerica, Mass., a large manufacturer of radiopharmaceuticals used in medical research.

Abraham said that the NRC has sent a radiation specialist from Philadelphia to look into the incident and added that preliminary investigations had determined that the vial "had probably not been lost more than 24 hours."

Abraham said that a U.S. Priority Transport driver had looked over his logs and routes and had delivery receipt signatures for every item except that which was supposed to be received by Fort Detrick.

D.C. officials said the city's radiological health specialist was also looking into the incident. The cardboard carton and the plastic container that should have covered the lead casing have not been found, said Abraham.

"There was no contamination and the students would have had to hold the vial for a day and half before you would have even seen a slight reddening of the skin," said Abraham. "We want to understand as much about this as we can. We want to find out how it came to be on the street."