Three students at Washington-Lee High School in Arlington were hospitalized last night -- one in critical condition and two in serious condition -- apparently suffering from overdoses of what county police believe to be one or more prescription drugs that were brought to the school.

In addition to the three students admitted to Arlington Hospital, authorities said a fourth was treated there and released.

Police said they believed it likely that all the students took the tranquilizer Valium, and possibly another drug that might also have had a depressant effect.

Police Lt. Gilbert Haring of the police youth resource unit said he understood that a male student apparently brought the drugs to the school at 1300 N. Quincy St. and sold or gave the drugs to others.

The four victims, described as two boys and two girls, were taken to the hospital by county ambulances between 8:30 a.m. and noon. None of their names was released. Haring declined to say last night whether the youth who allegedly brought the drugs was among those who were treated.

Haring said he understood that the youth who brought the drugs held a part-time job in a pharmacy, but police officials said last night that they did not know where and how the drugs were obtained.

After the incident, police said they made a search of lockers at the school and confiscated material they believed to be drugs. They said the unidentified substances will be tested in connection with the overdoses.

"We are quite concerned," county school Superintendent Charles E. Nunley told a reporter last night.

He said he telephoned all members of the School Board in connection with the incident and remained in touch with the school's principal, William Sharbough, through the day.

Sharbough could not be reached immediately for comment. Assistant Principal Dayna Smith declined to comment and referred inquiries to the police.

The first youth, believed to be the most seriously affected, was taken to the hospital around 9 a.m. Students said they understood that one student had earlier found him incoherent. Another student said he saw him wandering outside the school, seeming dazed, during an early class period.

Next, two students, apparently the two girls, were taken to the hospital some time after 9 a.m., and the fourth student, believed the least seriously affected, was taken around 11 a.m., according to one student's account.

One teacher said he learned about the incidents only after all students had been taken to the hospital, and that school routine was not affected.