District police set up roving roadblocks throughout the city yesterday and arrested more than 300 persons in the first department-wide attack on drug dealing in the nation's capital.

Assistant Police Chief Marty M. Tapscott said late last night that others were still being processed at several police districts. Another police official said that the number of arrests could be as many as 400.

The roadblocks, which employed a variety of police vehicles including a tractor-trailer truck, scooters, cruisers and vans, were established near areas where police say heavy drug activity is known to take place.

The operation, called "C-Note, Sevenfold," was "not directed at major drug dealers," Tapscott said in an impromptu press conference last night at police headquarters. "This is to disrupt the street sales of heavy narcotic traffic."

About 80 percent of yesterday's arrests involved drug-related charges, Tapscott said. However, most of these arrests were for possession of drugs and were made by officers observing activity near the roadblocks rather than of persons actually stopped, officials said. Most of the other arrests involved licensing violations, Tapscott said. There were also arrests for drunk driving and disorderly conduct, he said.

The seven-hour operation, which began about 2:30 p.m., involved at least one roadblock at all times in each of the seven police districts. In the afternoon and early evening, some roadblocks were moved. Police declined to give all locations, but three were along 14th Street NW at H and W streets and Florida Avenue.

Although individual police districts have earlier used the "disruptive technique," Tapscott said, "this is the first time all seven districts have done it at the same time" to combat drug trafficking. He said yesterday's operation was "very successful."

Most of those arrested yesterday were released on citations, Tapscott said. However, many are expected to appear in D.C. Superior Court on Monday, according to officials there. Judges and members of the U.S. attorney's office had been told in advance to expect a crush of several hundred cases early this week, sources said.

Yesterday, as cars reached the roadblock at 14th Street and Florida Avenue NW, police asked drivers to show their drivers' licenses and registration slips. Police checked the names against a five-inch-thick computer printout that listed the names of wanted persons. Officials said four fugitives were arrested and several warrants were served.

As the roadblocks served to discourage vehicle traffic through an area, plainclothes and undercover police officers scoured the adjoining streets to observe drug sales and make arrests, officials said.

Officials would not divulge how many officers took part in the citywide effort. Additional administrative personnel were also called in to keep up with the paperwork generated by the arrests, and Special Operations Division officers helped coordinate the roadblocks.

Police reported that they confiscated drugs, including marijuana, heroin and cocaine, and four handguns.

One man arrested at 14th Street and Florida Avenue NW complained that "the police aren't doing much with this operation." The man, who asked not to be identified, was arrested on a charge of driving without a license, taken to the 3rd District station and booked. The man later said he was treated callously, then released.

"They can't stop us," said a tall man wearing a white and black sailing cap and standing among a crowd of people in the 1400 block of W Street NW. "We're trying to survive. Ain't no jobs out here. You got to get out here and make it best you can."

Standing on the opposite side of the street, Maurice Proctor-Bey, 26, and his son, Maurice Jr., 8, watched cars roll through the police checkpoint.

"If the police can stay on this and make a dent in the drug business in this town, I'd be glad. With every arrest they make, there's a better chance of my son making it out here. . . . "

Officials said the name of the operation came from Deputy Chief James Kelly of the 7th District, who used the "C-Note" term there and suggested the citywide effort. "Sevenfold" refers to the seven police districts.