Roy E. McKoy, a 61-year-old Marshall, Va., restaurant owner, pleaded guilty yesterday in U.S. District Court in Alexandria to a single misdemeanor count of refusing to serve a customer in 1983 because the customer was black.

In exchange for the guilty plea, six similar misdemeanor charges against McKoy and a single charge against his wife Patricia were dismissed.

McKoy is scheduled to be sentenced March 8.

He could receive a maximum penalty of six months in jail or a $1,000 fine.

McKoy and his wife were also found in civil contempt yesterday of two previous federal court orders, issued in 1967 and 1974, directing them to serve blacks. McKoy was jailed briefly in 1967 for his failure to comply with the order issued in that year.

At a 25-minute hearing, Judge James C. Cacheris ordered the McKoys to post a sign in their establishment, the Belvoir Restaurant, announcing that they will serve blacks.

He also ordered them to take three newspaper ads announcing that blacks are welcome at the restaurant, post a $500 cash bond, report to the U.S. attorney the number and race of the customers they serve each month for the next two years and pledge in writing to serve blacks in the future.

During a similar court hearing in 1967, McKoy declared that constitutional protections do not apply "to the dark people."

Yesterday, the McKoys' attorney, Thomas L. O'Neill, said they "absolutely intend" to comply with the latest order. "They did it last time, and they will do it this time."

He said the McKoys have served blacks in the past, but acknowledged that they have refused to serve blacks on some occasions.

If the McKoys fail to comply with the order, they can be fined $100 a day.

The McKoys' small, roadside cafe is attached to their home on Route 55 in a sparsely populated area about 50 miles west of Washington.

Cacheris's order resolving the civil contempt portion of yesterday's hearing was nearly identical to the one issued in 1974, when the McKoys were found to have violated the 1967 decree.

The only new section is the requirement that the couple take three ads in a newspaper in Fauquier County stating that their restaurant "serves everyone regardless of race, creed or color."

Both McKoy and his wife originally pleaded not guilty to the eight-count federal indictment and were scheduled to be tried Feb. 20. The guilty plea was arranged yesterday just before a hearing on routine motions in the case, attorneys involved said.

The McKoys refused to comment.

O'Neill said their business has been sparse since I-66 opened and took traffic from the rural highway on which they are located, but that the couple continued to support themselves from the restaurant.

The charge to which McKoy pleaded guilty involved his refusal to serve Alvin C. Talley, who is black, on Sept. 24, 1983.

According to a statement Talley gave federal prosecutors, he was working as a chauffeur and stopped between duties at the restaurant for supper.

"After sitting at a table for a minute or less, a white male approached me and asked, 'Are you invited here?'" Talley said in his statement.

Talley said that when he responded "no," the man told him to "get out," and he did.

[Chan Kendrick, executive director of the Virginia American Civil Liberties Union, said a civil suit the ACLU filed against McKoy alleging that he violated constitutional protections is still pending, United Press International reported. Yesterday's court action "just helps our case," Kendrick said. "We asked for a jury trial and we will let the jury decide."]