Two Northern Virginia men have been arrested and charged in connection with the illegal manufacture and sale to federal undercover agents of pipe bombs, one of which was described in court documents as big enough to "down a building."

The pair were arrested at their homes late Thursday after a month-long investigation by Bureau of Alcohol, Tobacco and Firearms agents using hidden radio transmitters to eavesdrop on conversations between undercover officers and the suspects.

Charged with the illegal possession of unregistered firearms were Randolph H. McGavran, 25, of 6814 Edsall Rd., Fairfax, and Monte Lee Hall, 29, of 2111 Rollins Dr., Alexandria.

Affidavits filed by authorities in federal court in Alexandria said three bombs -- two of them using a highly sensitive mixture of black powder and plastic explosive -- were sold or given to the agents in exchange for cash and promises of methamphetamines, a narcotic known on the street as "crank."

One of the bombs later was exploded by Virginia State Police bomb squad members and hurled metal fragments some 55 yards, according to the affidavits. A second bomb, containing 5 1/2 pounds of black powder and a half-pound of plastic explosive, also was detonated by Army bomb experts, officials said.

According to court documents, McGavran was contacted by agent Joseph D'Angelillio on Oct. 14 after an unidentified informant told law enforcement officers McGavran allegedly was willing to trade explosive devices for drugs.

D'Angelillio, posing as the brother of a Philadelphia drug dealer, subsequently bought two bombs and a one-pound block of C-4 military high explosives from McGavran, the government charged.

After his arrest, the affidavits said, McGavran agreed to cooperate with the agents and gave a statement implicating Hall as the manufacturer of the devices.

Documents filed in connection with a search warrant for Hall's residence said agents found traces of smokeless powder, threaded pipes and caps, batteries, modeling clay and a home-made circuit tester on a workbench.

At one point during the investigation, agents followed McGavran and two other men as they drove in a pickup truck to the Delta Gun Shop in Manassas, the documents said. Once there, the three bought five one-pound cans of black rifle powder, unaware that a clerk in the store, James P. Ford, was an undercover Alcohol, Tobacco and Firearms agent.

McGavran and Hall face a maximum penalty of 10 years or a $10,000 fine or both.