The Montgomery County Board of Education voted yesterday to order drug tests of all school bus drivers in a tough new policy that reflects growing concern about student safety.

The policy, opposed strenuously by the union representing the county's 1,000 drivers, will require job applicants to undergo a urine test for alcohol and illegal drugs, starting next month.

All drivers also will be compelled to take a drug test during an annual physical examination, as of July. Additional tests will be ordered if drivers are suspected of using drugs or if their buses are involved in any kind of accident, including one in which the vehicle is parked.

School officials said yesterday they have little evidence of drug abuse among drivers. But employees who refuse a test will be assumed to have used drugs, be considered insubordinate and may lose their jobs, the policy says.

School board members voted to start the tests, estimated to cost $20,000 to $25,000 a year, after debating the balance between employees' privacy rights and children's safety.

"I have some concerns with the intrusiveness of this, but we also have to talk about accountability," said Frances Brenneman, a board member who supported the tests. "We are talking about our children being transported safely."

Board President Blair Ewing cast the sole dissenting vote after arguing that the school system's bus safety record did not warrent the tests. "I think there are some serious constitutional issues that relate to this, including privacy issues . . . . Until you have clear evidence there is a problem, you ought not mandate testing."

According to school officials, Montgomery has fewer than 200 bus accidents a year, most of them minor. During the last few years, a handful of bus drivers have been dismissed or transferred to other school system jobs because of problems with drugs or alcohol.

The new policy is not the result of any specific bus accident or evidence of irresponsible driving. It is the outgrowth of labor contract negotiations that started in 1987, about the time of several well-publicized transportation accidents, including a fatal Amtrak crash near Baltimore in which a train engineer was found to have been under the influence of alcohol.

"No justification has been shown," complained Vincent Foo, president of the Montgomery County Council of Supporting Services Employees, the union representing drivers.

"Everybody is against drivers using drugs, including the drivers," Foo said, adding that he did not object to tests for new applicants or for drivers suspected of abusing alcohol or using illegal drugs. But, he said, "The burden should be on the employer to establish just cause for discipline, not on the employee . . . . We have people who have been driving 20, 25 or 30 years who do not have problems with drugs."

"I don't like it," said Marion Haupt, 33, a bus driver in Germantown who has worked for Montgomery for 12 years. "I don't think there's a cause for it either. I don't see it out there among us. I feel like I have to prove I am a good employee and a clean person just to satisfy them, satisfy the public, that they run a tight ship."

Montgomery's new policy is part of a growing concern about students' safety while they ride to school.

The Maryland State Department of Education has formed a task force to study the issue. The group is recommending some form of bus driver tests statewide, although the details have not been resolved, said Robert Slade, the transportation director in Prince George's County, who belongs to the group.

In Prince George's and Prince William counties, drivers may be tested if their supervisors suspect drug use. In Fairfax County and the District, bus drivers must undergo a physical exam before they are hired and an annual test after they start work. As part of the examination, a doctor must certify that the driver is drug-free.