A D.C. school bus aide who was fired after she received a positive result on a urinalysis for marijuana use filed suit yesterday in U.S. District Court here to get her job back.

Juanita M. Jones, 49, one of 35 part-time aides fired last August by the D.C. school system, contends in the civil suit that the drug test results were inaccurate and the decision to fire her was "arbitrary and capricious."

In the lawsuit, which names D.C. School Superintendent Floretta D. McKenzie, school official William J. Bedford and the District, Jones is seeking reinstatement, back pay and $150,000 in damages.

Lawyers with the American Civil Liberties Union who, along with another law firm, are representing Jones, said the suit is a "test case on several issues," including the accuracy of drug tests and the right of governments to use them as a basis for dismissal.

School officials, citing an increased number of school bus accidents, began testing employes during annual physicals last summer for marijuana, cocaine, PCP and heroin use.

Two full-time drivers also were suspended as a result of the tests, but both have since passed new tests and have been reinstated, according to Maurice Sykes, school system spokesman. Sykes would not comment on the lawsuit yesterday.

Regular urinalyses and occasional spot checks are still being performed, he said, "to make sure that people are clean who are driving. It remains an issue of safety."

Jones, who lives in Northeast Washington, was hired as a school bus attendant for handicapped students in 1981.

In a recent interview, Jones said she had smoked marijuana only once in her life -- 13 years ago.

"That was the first time, and that was the last time," she said.

Her lawsuit challenges the so-called EMIT test, which detects THC, the active ingredient in marijuana.

At issue is whether a positive result on the test violates the D.C. school system's policy that prohibits using or possessing alcohol or illict drugs or being under their influence while on school property.

The EMIT test, manufactured by the Syva Co. of Palo Alto, Calif., detects "recent use" of marijuana, according to company spokeswoman Michelle Klaich.

Recent use is usually up to five days, but can be as many as 10 days, Klaich said.

In rare cases, she said, the test also can detect THC in people who were in a room where marijuana was smoked.

In the lawsuit, Jones contends that the test has a "substantial degree of inaccuracy."

A study conducted by the national Centers for Disease Control in Atlanta found that 4 percent of the samples that tested positive were "false positives," or drug-free.

Another study, by the Air Force, which also uses the test, found up to 11 percent false positives.

Jones' suit also contends that test samples were sloppily handled and may have been "confused, mislabeled, or both."

Klaich said that in any case "where rights or responsibilities are at stake" -- such as firing -- Syva recommends confirming the test results, usually with a second, different test.

That step was not taken in the Jones case, according to court papers.