When Christopher Gore tried to enlist in the Coast Guard in 1994, he was rejected for having a history of drug use.

But the clean-cut Dillard, Ga. youth was no junkie. The drug he had used was Ritalin, a medication prescribed for attention-deficit disorders.

Scores of young men and women across the country are learning that the Ritalin they took as teenagers is stopping them from serving their country or starting a military career.

"I was shocked and disappointed," said Gore, 22, who is about to start a job selling radio ads. "I didn't expect [Ritalin] to affect my future like this."

Though the Pentagon hasn't tracked the number of people rejected for military service because of Ritalin use, policy planners are increasingly concerned about Ritalin's effect on the future of the military -- particularly in light of the escalating use of Ritalin among schoolchildren. "Ritalin use is a problem for us because we want to qualify as many quality people we can for military service," said Lt. Col. Ed Baldwin.

All branches of the armed forces reject potential enlistees who use Ritalin or similar behavior-modifying medications.

A long-standing Department of Defense directive also instructs the military to reject those with a "chronic history" of an academic skills defect -- including ADD -- after age 12. And people who took Ritalin as teenagers to treat ADD, an inhibitor of academic skills, are rejected from military service, even if they no longer take the medication.

Master Sgt. Cruz Torres, a Marine recruiter, said that at least 1 out of an average of 50 potential recruits who are interviewed every month is rejected because of past or current Ritalin use.

"Unfortunately, there's nothing we can do if a person has been using Ritalin," he said. "It's considered to be a mind-altering drug. Because of that, the services look at it as a very, very serious drug."

Sgt. Carl Voss, a local Air Force recruiter, said he, too, sees one or two potential enlistees disqualified each month because of Ritalin use. If a person struggled in school with ADD, chances are slim for success in the Air force," he said.

"The Air Force is very selective," he said. "All of our classes are college level."

Parents, doctors and teachers are largely unaware that the military services are exempt from the American Disabilities Act and can discriminate against people using such behavior-modifying drugs as Ritalin, recruiters say.

Harold and Jane Gore had no idea that allowing their son to take Ritalin would someday sink his hopes to enlist in the Coast Guard.

The Gores maintain that their son was never hyperactive. But because they were concerned about his academic performance, they took him in 1984 to an Atlanta pediatrician.

The doctor prescribed Ritalin to improve the youth's concentration. Christopher took 10 mg of Ritalin daily from 1985 to 1988 while a student at St. Francis Day School, in Roswell, Ga. He took the medication intermittently through 1991.

A Coast Guard recruiter interviewed Gore on Dec. 22, 1994. Gore passed written and physical tests. When asked about prescription drug use in a questionaire, he mentioned Ritalin.

On Jan. 24, 1995, he was disqualified.

"It was a real disappointment," Gore recalled. "And the irony is that I never wanted to take Ritalin in the first palce."

The Coast Guard recruiter requested a medical waiver for Gore noting his "eagerness to enlist" and his above average scores in math and reading comprehension. The waiver was denied. "Use of Ritalin after age 12 years," was cited as the reason.

Gore said he later met a group of Marine recruiters who encouraged him to enlist. They advised him not to disclose his past Ritalin use, he said. But the recruiters subsequently found that Gore's medical disqualification had already been extended to all branches of the military.

Since 1990, the use of Ritalin nationwide has increased sixfold. The U.S. Department of Education estimates that 3 percent to 5 percent of all children under the age of 18 have ADD.

The burgeoning use of Ritalin is prompting military planners to take a closer look at ADD and how it might affect future manpower needs. The Pentagon is studying the training the training-camp performance of former Ritalin users who enlisted with the help of a medical waiver, said policy-planner Baldwin, a medical doctor.