The Virginia Capitol, scene of such memorable events as the Aaron Burr treason trail and Robert E. Lee's acceptance of his Civil War command, today had its first drug bust.

In a bold daylight raid, a uniformed Capitol policeman and two plainclothes Richmond vice squad officers nabbled marijuana lobbyist Roy Scherer, 35, and a three-inch marijuana plant.

The plant was potted in a plastic panty hose container and Scherer was carrying it from a meeting of the House of Delegates Courts of Justice Committee to the House Health, Welfare and Institutions Committee when he was arrested.

Scherer had laid most of the investigative foundation for his own arrest. His five-year advocacy of liberalized marijuana laws in Virginia, including countless apearances before legislative committees, had established his identity beyond doubt with Capitol policemen.

Scherer als had established the identity of the scraggly plant in the panty-hose container. On Thursday night, after using it as an exhibit during testimony before a Health, Welfare and Institutions Subcommittee, he turned it over to the Capitol police and told them, "This is marijuana, contraband. I am turning it over to you in accordance with the law."

Scherer said in an interview after his arrest tht he did not ask the Capitol police to keep the plant for him, but when he returned today he inquired whether they still had it.

"When they said they did, I asked them if I could take it down to the meeting of the full Health and Welfare Committee," Scherer said. "They said it would be OK, but the officer suggested I cover it up as I carried it through the halls."

Such friendly advice conforms to the best traditions of the Capitol police. They are responsible for security at the Capitol and nearby government buildings, but during legislative sessions they gallantly serve as armed ushers to the crowds of citizens and lobbyists that swarm the seat of government.

They are conspicuous in the aid of legislators ginerly parking Cadillacs and Lincolns on the crowded Capitol driveway.

The routine of such benign service apparently has dulled the investigative instincts of some officers because it was some time before they recognized the threat posed by Scherer's potted plant.

The lobbyist sat for nearly an hour waiting his turn to testify in two committees before he and his plant were detained. He was charged with possession of marijuana, a misdemeanor that carries a maximum penalty of one year in jail and a $1,000 fine. He was immediately released after being served with a summons, a procedure adopted by the Assembly partly as a result of lobbying by Scherer.

Scherer represents the Virginians for Study of Marijuana Laws. The purpose of his testimony today was to presuade legislators that possession of marijuana plants should not be accepted as evidence of attempt to manufacture dangerous drugs, a crime that is punishable by up to 40 years in prison.