The former live-in gardener of Virginia Lt. Gov. Charles S. Robb has been indicted by a federal grand jury in Alexandria on charges of possessing 12 ounces of cocaine with intent to sell it to an undercover narcotics agent, federal officials reported. That amount of the drug, if pure, could retail for about $500,000, a drug enforcement official said.

The suspect, Jean Michel Bardet, 26, lived at the Robb's Mclean home during part of the several weeks he was under investigation, according to a spokesman for the U.S. Drug Enforcement Administration. He is accused ofpossessing 12 ounces of cocaine in an apartment at 12001 Courthouse Rd, Arlington, and using the telephone in an effort to it to an undercover narcotics agent.

Bardet, who was employed by the Robbs as a gardener and domestic worker, lived at their home with his girlfriend, Brenda Kay, another Robb employe, according to his attorney, A. Anthorny Giangreco.

In an unusual move during a bond hearing yesterday, U.S. District Judge Robert R. Merhige suggestedthat Kay be included under Bardet's $50,000 personal recognizance bond and Kay agreed to the arrangement, Giangreco said. Kay is not in the case.

"She has a legal obligation to contact the court if Bardet's whereabouts are unknown," said Assistant U.S. Attorney Henry Hudson. If Bardet flees, Kay could be held in contempt of court and couldbe liable for part of the bond, Hudson said, adding, "I've never seen anything like it."

The DEA spokesman said Robb was unaware of Bardet's alleged drug connections whenBardet lived at his home and cooperated fully when he waslater advised by police of the investigation.