The Defense Department has begun testing all military recruits for drug and alcohol abuse.

All enlisted recruits as well as officer candidates applying to the military academies and Reserve Officer Training Corps program will be tested for alcohol, marijuana and cocaine.Applicants attempting to join the National Guard and the reserves also will be tested.

Congress ordered the drug testing program last December when it approved the Pentagon's fiscal 1988 budget bill, requiring that it start by the first week of June.

Defense Secretary Frank C. Carlucci decided last January to start the testing at military processing stations around the country on June 1.

"Positive findings for marijuana and alcohol will result in an enlistment ineligibility for six months on the first test," the guidelines state. "Positive findings for cocaine will result in an enlistment ineligibility for one year. A positive second test on any of the three drugs will result in a two-year period of enlistment ineligibility."

The Army, Navy, Marine Corps and Air Force signed up almost 317,000 recruits in fiscal 1987.

The testing has been opposed by some officials in the Defense Department on grounds it is too expensive as well as unnecessary, since all military personnel on active duty face random drug tests at any time.

A teen-ager planning to join the military can abstain from drugs for a brief time and probably pass the test, noted one manpower official, who asked not to be named.

Congress approved a budget amendment sponsored by Sen. Ernest F. Hollings, D-S.C., who said that "a drug-screening program is logical and long overdue."

"The time to start catching the users is before they join the armed forces, when the government has no obligation to them," Hollings said.

Carlucci, in setting out test guidelines, concluded recruits should be tested "for drug and alcohol use during their pre-enlistment physical examinations," using a breathalyzer or blood alcohol test for alcohol detection and urinalysis for marijuana and cocaine detection.

The standard for alcohol impairment will be a blood alcohol level of .05, the directive said.