On the ninth floor of a building near the White House, one of the government's less visible investigative staffs churns out thousands of reports each year.

It's the Division of Personnel Investigations, the arm of the Office of Personnel Management that checks the backgrounds of more than 200,000 federal job applicants each year.

The office has been around for 30 years, since President Eisenhower decided the government needed a way of preventing communist infiltration of the bureaucracy.

"True, we were created . . . in the aftermath of the McCarthy hearings, but our mission has changed greatly over the years," said Peter Garcia, who has directed the office for the past three years. "We're not looking for communists now as much as we're looking for characteristics in a person's background that do not make that individual a good prospect as a federal employe--such as heavy drug use or theft, with or without a conviction."

In fiscal 1982, the 860 staff workers in Garcia's office screened 225,000 applications. Four hundred employes are investigators, 200 of which work out of small offices around the country.

Presidential appointees and Energy Department employes are checked by the FBI, and candidates for sensitive jobs with the Defense, State and Treasury departments and the U.S. Postal Service are reviewed by investigators with those agencies. But Garcia's office handles the rest, including 25,000 applicants for sensitive jobs at other agencies.

Eight out of nine of the applicants screened by OPM were given only the basic check, the National Agency Check and Inquiry, and usually after the person was already on the job. This survey involves little more than sending forms to an applicant's former employers, the schools he attended and the police departments in places where he lived. Each survey costs OPM between $9 and $20, depending on whether a credit search is necessary.

"We check on questions of performance, of loyalty . . . ," Garcia said. "Our goal is to give the agency advice on whether that individual is suitable for federal employment."

A federal job is always contingent on passing the review, and in about 1,000 cases, Garcia's office recommends that the employe be fired or kept under supervision for awhile. Only rarely do investigators turn up something so dramatic that they say the employe must be fired. In most cases, the hiring agency makes the final decision--one reason Garcia doesn't know how many applicants fail their security checks.

"There's a lot of discretion involved," he said. "If someone hit someone with a car 25 years ago, should that stop them from being employed? Maybe as a government driver, it would, but not in most cases."

Garcia said that over the years court decisions and changing life styles have made hiring practices more relaxed than they once were. Homosexuality, for instance, is no longer a barrier to federal employment, Garcia said, except for some of the most security-sensitive positions.

"And even for that security-sensitive position," Garcia said, "it may become a legal question about whether he is in or out of the closet."

For the more sensitive jobs, the checks are more elaborate. Called BIs (for background investigations going back five years) or SBIs (for special background investigations going back 15 years), these checks send investigators into the field to ask some of the same questions in person. All of the OPM reviews include a check of the FBI's criminal fingerprint files.

The OPM charges other agencies between $1,450 and $2,200 for each of these more detailed checks, depending on how elaborate they have to be and how quickly the information is needed. About 15,000 are performed annually for the Energy Department for contractors who have access to nuclear secrets. The Justice Department is also a "major customer," requiring about 6,000 checks a year.

The charges have upset some of Garcia's clients, including the State Department and the General Accounting Office. GAO is looking for a private contractor to do the job, in the hope that it can cut in half the $250,000 it spent on security checks last year.

Garcia said the Reagan administration is now considering setting tougher hiring requirements and creating two more levels of security investigations. The proposals, he said, are on the desk of OPM Director Donald J. Devine.