Eighty-one persons were arrested yesterday at roadblocks at two sites and at other locations throughout the 7th Police District in Southeast Washington during another phase of the citywide crackdown on drug trafficking, D.C. police said.

Yesterday's eight-hour operation, called Operation C-Note, followed by about two months a similar, city-wide effort called C-Note Sevenfold, which sparked opponents to petition for a referendum on such use of roadblocks. If the petition drive is successful, the issue will be on the November ballot.

Police said about 80 percent of yesterday's arrests were for drug-related charges. Although a precise breakdown of the arrests was not available early this morning, police said most were misdemeanors, such as possession of marijuana, PCP, heroin and cocaine and sale of marijuana. There were also some arrests on felony charges, including sale of PCP, police said.

About 10 of those arrested were sought on fugitive or bench warrants, according to police officials. They said about 30 persons remained in custody pending appearance in court Monday.

The operation, which began about 2:30 p.m., involved more than 100 officers, including about 40 in uniform and the rest in civilian clothes, police said.

As in the citywide operation in July, police used a roadblock as a diversionary tactic, drawing attention away from officers in plain clothes who observed alleged drug transactions nearby. The roadblock initially was set up at 16th and U streets SE, and was moved four hours later to 15th Street and Robinson Place SE.

Police said several hundred persons were stopped at the two roadblocks, and about 30 of those were arrested, police said.

Most arrests, however, were made after officers in casual clothes observed alleged drug transactions and radioed descriptions of people or vehicles to other officers nearby, who stopped suspects as they left the scene.

In addition to the roadblock locations, the operation was carried out near two housing projects, Barry Farms at Sumner and Wade roads SE and Condon Terrace at Sixth Street and Condon Terrace SE, police said.