Three Washington-Lee High School students hospitalized in serious condition after apparent drug overdoses Thursday probably were affected by the combination of drugs used rather than by the dosages, Arlington police said yesterday.

Police said they believe the three students, as well as another who was treated and released from Arlington Hospital, took the tranquilizer Valium and another prescription drug with sedative effects.

The students may not have realized that the second drug was a depressant that would aggravate the effects of Valium, police in the vice control and youth resource units said.

Police also said that a male student who allegedly brought the drugs to the school at 1300 N. Quincy St. was among those hospitalized.

The names of the four students, who are 15 or 16 years old, are not being released because they are minors.

Arlington Hospital spokeswoman Deborah Proud said all three students, one boy and two girls, were in intensive care late yesterday.

Proud said the students' families had requested that no further details about their conditions be released and said she had "no idea" how long the three would be hospitalized.

Police said they seized some prescription pills in a search at the school Thursday but would not say yesterday how many pills were recovered. "An effort was made to locate all the drugs that may have been involved. We don't know if we got them all," said Sgt. David Tooley of the youth resource unit.

Officials said they still do not know the answers to some important questions, including the source of the drugs, the dosages and whether they were sold or given to the students. Police said the investigation would continue through next week.

As students poured out the doors of the high school yesterday afternoon, their last day before a one-week vacation, talk of spring weather and crew practice was mixed with chatter about Thursday's events.

Principal William Sharbaugh, stationed with other administrators in a first-floor corridor shortly before the final bell, refused to discuss the overdose cases and referred a reporter's questions to police.

Although no formal announcement about the incident was made in school, students said the news spread quickly Thursday and described the general reaction as "shock" and "surprise."

Most students described the overdose cases as unusual, but a few said drug use at the school seemed to have worsened recently. "There are more people leaving to get high during lunch," said freshman Brad Missal.

Police have not been able to interview the three students who are hospitalized, but interviews with other students indicate the incident was "an isolated case," said Elwood Hibberd of the vice control section. "The people involved apparently knew each other. It was not an outside source coming in and selling drugs to these kids."

An Arlington Hospital counselor who works with drug-dependent adults said the hospital does not keep statistics on juvenile drug abuse. But, she said, "It doesn't matter if it's Arlington or Fairfax or wherever. There are drugs in every school. We see adolescents who say, 'School is where I go to get high.' "

Martin Wasserman, director of the Department of Human Resources in Arlington, said, "I wish there was some way you could tell these kids: 'This is the big casino. You can't just fool around popping different drugs and expect that everything is going to be okay. This stuff is no game.' "