Loudoun County school students in grades six through 12 who are suspected of having consumed alcohol will be subject this year to the same breath analysis tests that police use to detect drunk drivers. School Board Chairman William J. Maykrantz Sr. said the system was acting to give principals "an additional tool" to detect intoxicated students.

Students found to have any blood-alcohol content will be subject to disciplinary action ranging from after-school detention to 10-day suspension, as will students who refuse to submit to the test, under a new policy effective when the schools open Monday.

"We've continually had to say somebody's come to school under the influence, and in all fairness to these people who are being accused, we will now have a way to be sure," said Loudoun Superintendent Robert E. Butt. He said the devices will be used "only after reasonable cause is shown," either through a student's behavior or because his breath smells of alcohol.

The action makes Loudoun the second school jurisdiction in the Washington area to use such testing. A Fairfax County school official said late yesterday that the system, the largest in the Washington area, made an unannounced purchase of 25 breath analysis devices three years ago and provided them to every high school in the county. She said the devices have been used, but she did not know how frequently.

Area school officials have expressed concern in recent years about the increasing use of alcohol by teen-agers. Students in Loudoun, Fairfax and most other systems in the country are forbidden to possess or consume alcoholic beverages on school grounds, and also are forbidden to come to school under the influence of alcohol. Virginia law forbids those under age 19 from purchasing or possessing alcoholic beverages.

Civil rights and education groups contacted yesterday expressed surprise at the testing plans, but did not voice any objections or denunciations.

Officials of the National Education Association and several other national groups said they were unaware of any other school systems in the country that subject their students to the breath analysis procedure.

Fairfax's breath analysis equipment was acquired and distributed without fanfare three years ago, in contrast to Loudoun's current course. "We're going to be giving it additional publicity, as far as sending home information to parents and students," Butt said. Use of the devices will not begin until about two weeks after school opens, he said, a delay designed to give students adequate warning of the policy.

Arthur Welch, Loudoun's assistant superintendent for planning and pupil services, said the point of acquiring the devices is to discourage students from drinking in the first place.

"A lot of our interest in this is that if kids know that they can be tested, they are going to be less likely to consume alcohol on the way to school," Welch said. "We are a lot more interested in keeping kids from using alcohol before they come to school than in catching them afterwards."

He said that any student who refuses a request to take the test is likely to be suspended for violating a policy that requires students to obey the orders of school officials.

Loudoun, which has 13,000 students in its schools, 7,500 in middle and high school, purchased 10 "Alco-sensors" for $300 each, and each middle and high school was provided with one. Virginia State Police, who use the devices to make initial determinations about suspected drunken drivers, have trained school officials to use them.

The Alco-sensor, manufactured by Intoximeters Inc. of St. Louis, is about the size of a pocket calculator. Those suspected of having consumed alcohol breathe into a disposable, 11-cent mouthpiece, and the device provides a two-digit read-out of percent of alcohol in the blood.

Loudoun high school principals were in a meeting yesterday afternoon and unavailable for comment. Assistant principals at several schools said they were happy to have the new instrument, but did not expect to have to use it frequently.

"My guess would be that if we used it a half a dozen times a year it would be a lot," said Michael Martin, assistant principal at Loundoun County High.

He said that principals had requested the device. "We did want it, yes," Martin said, "because we are in the position of having to deal with kids who may or may not be intoxicated, and we have never felt comfortable without proof. When we call up a parent and say, 'Your child has come to school under the influence,' we need to feel a whole lot more secure than, 'We guess,' or, 'we think.' "

Loudoun High has an automatic suspension policy for students who come to school under the influence of alcohol. There were five such suspensions at the high school last year.

All school system officials said they have no plans to use the devices to test students randomly or on a wholesale basis. "We're not going to be sticking it in every kid's mouth on the first day of school or anything," Martin said.