More than 600 D.C. special education students waited in vain for school buses yesterday morning because 20 percent of the city's bus drivers and attendants stayed home in what city officials called an illegal union "sickout."

A union leader denied that a strike had been called but complained that the school system has ignored chronic payroll problems.

David Gilmore, the District's court-appointed school transportation administrator, said that about 260 of 1,300 drivers and attendants called in sick, affecting about 13 percent of daily bus routes. Some parents drove their children to school; other students were forced to stay home.

The District uses school buses almost exclusively to transport D.C. special education students to public and private schools. Many of the children have severe disabilities and use a wheelchair, requiring an attendant to help them board the bus. On an average day, 4 to 5 percent of drivers and attendants call in sick, Gilmore said.

Bus drivers and attendants have had longstanding grievances about pay. For years, they have complained that paychecks are sometimes issued in the incorrect amount -- or not at all. Furthermore, a new contract negotiated 18 months ago called for step increases that some of the workers are not receiving.

"Some of them have some legitimate grievances. . . . But in an act of desperate abandon, some of them participated in a 'blue flu' today, a sickout," he said, adding that it is illegal for a public servant in the District to strike.

George Johnson, executive director of District Council 20 of the American Federation of State, County and Federal Employees, which represents Local 1959, the drivers' and attendants' union, denied that any strike or work stoppage had been called.

He said that all of the 260 drivers and attendants who did not come to work must have been sick.

"I'm not sure why people are calling this a strike," he said. "I think a lot of people got sick and didn't report to work today. . . . No public employee in the United States has the right to strike. Nobody called any strike. We don't condone strikes, work stoppages, sickouts."

He said, however, that the school system had not been negotiating in good faith about its efforts to fix the payroll problems.

"It takes no system a year and half to correct the problems we are facing," he said.

Several bus drivers who worked yesterday said they had been asked by the union to call in sick. They spoke on the condition that they not be identified, saying they feared repercussions from the union. Another driver working yesterday, Roderick George, declined to comment on whether he had been asked to call in sick but said he had a "different agenda."

"I have a commitment to these children," George said.

Gilmore said any driver or attendant who did not show up for work yesterday will be required to present a doctor's note detailing why. Anyone who cannot do so will face penalties that might include termination, he said.

"I won't blink an eye, and I won't miss a night's sleep," he said. "I have a lot of kids and parents to apologize to."

He also said school system officials were seeking a court injunction against the union to prevent work stoppages in the future.