Charles J. Allen used to work for the General Services Administration. After the federal government began an investigation of GSA contracting, he quit the job, was hired by the Department of Transportation and later admitted accepting $15,000 in bribes in return for certifying that GSA had received huge quantities of office supplies never sent.

Allen was given a four-month sentence. He served one month in jail on unpaid leave of absence, and spent the remainder of his term working during the day and staying in a detention center at night.

Now, pension benefits intact, Allen is back on the job, supervising a dozen employes and occasionally buying supplies for the government -- just one floor below his old GSA office in the Nassif Building in Southwest Washington.

Allen's fortunes illustrate what many regard as the mixed results of criminal investigations that began three years ago into GSA, a $7-billion-a-year agency that acts as the federal government's business manager.

In sheer numbers, the investigations probably represent the most successful attack on government corruption in history. So far, 91 individuals and corporations have been indicted, and more indictments are expected.

Eighty-seven of those indicted have pleaded guilty or been convicted. Three have been acquitted.One defendant is awaiting trial.

Most of the GSA employers and contractors involved have been sentenced to jail terms ranging from 20 days to six years. In addition, some have forfeited large sums in pension benefits and face civil suits and income-tax levies on their unlawful gains.

The investigations by the U.S. attorney's office in Washington and Baltimore are now winding down. A special Justice Department task force on GSA corruption is expecteed to close shop in six months.

The investigations have produced procedures designed to improve controls in the two areas most affected by the scandal -- supply purchases and the awarding of contracts to repair and alter federal buildings.

But for every improvement, there appears to be an uncorrected abuse. The new procedures for verifying receipt of office supplies for example, are often ignored according to internal auditors who conducted a spot check.

On Friday, the General Accounting Office, the audit arm of Congress, reported to Rep. John L. Burton (D-Calif.) that GSA's office supply centers continue to suffer from inadequate inventory controls, poor management, and potential for fraud.

"Overall, I see little improvement," Howard R. Davia, chief of GSA's office of audits, said last week. "We still have a significant level of waste and abuse."

"The fact that GSA now has an office of inspector general in progress, but things haven't changed that much," William S. Lynch, chief of the Justice Department task force, said. "There are still an incredible number of people over there who do their jobs with blinders on."

"Five years from now, we could have another GSA scandal," and FBI agent involved in the probes said.

It is this program -- called the multiple-award schedules -- that resulted in GSA paying more electronic calculators, television sets, and typewriters than what the same items sell for at retail outlets.

More than a year ago, the GAO said most of the 4 million items GSA purchases under the program should be put out for competitive bids. Until the GAO began checking on its recommendations last May for Sen. Lawton Chiles (D-Fla.), GSA had taken no "positive action" to put the recommendations into effect, the GAO said.

Since that time, GSA has put two items out for bids -- a small quantity of typewriters and photocopying paper. As a result of obtaining competitive bids for copying paper alone, GSA saved $1.6 million over a six-month period.

"Until we began our follow-up review (a year after the first GAO report was issued), GSA had not made any improvements that would solve the program's fundamental deficiencies," the GAO said.

After the probes of GSA's office supply centers began, the cost of supplies for the centers -- called self-service stores -- dropped by $25 million a year. Prosecutors attributed the drop to a reductin in the level of fraud and the fact that then Gsa aDministrator Jay Solomon ordered GSA to stop carrying items that had a high potential of abuse.

These items -- like Polaroid film and hand tools -- were being taken home for personal use or stolen by the carton and resold.

Recently, Freeman allowed each GSA region to decide what items will be carried, and many have again stocked their shelves with goods previously dropped.

"I find it discouraging that GSA is again offering things that can be easily stolen," said Elizabeth H. Trimble, the assistant U.S. attorney in Baltimore in charge of the office supply investigation.

When Freeman came to GSA he sought to minimize the extent of the scandal, saying it was "overblown." He later acknowledged that GSA has serious problems, but provoked more criticism by demoting William A. Clinkscales Jr., the GSA official who helped start the investigations. a

Clinkscales was chief of GSA's office of investigations and had 150 employes reporting to him. In his new job, he has no employes reporting to him and freely acknowledges having little to do in his $50,112-a-year position. h

Charles Allen, who pleaded guilty to defrauding the government, now supervises three times more employes as a copy facilities supervisor at DOT than he did at GSA. The agency paid him while he spent 90 nights at a detention center as part of his sentence.

A DOT spokesman said Allen's performance at DOT, which hired him before he was indicted, has been "satisfactory," and the agency felt he has been "rehabilitated." DOT decided to retain him after consulting with the Office of Personnel Management, the spokesman said.

Freeman did not return a reporter's telephone calls made over a period of three days last week. He then said he only would take questions in writing, although an aide said the answers would not necessarily be written by Freeman.

The investigations of corruption at the General Services Administration began in 1977, when Internal auditors of the Internal Revenue Service noticed that an IRS office in Cleveland was being charged by GSA for large quantities of photocopying paper not used by IRS copying machines.

The investigations uncovered an almost limitless variety of payoffs received by GSA employes. They included cash, color television sets, trips, furniture, clothing, appliances, and free painting work.

The sums involved were often staggering. Contractor Carmen O'Connor admitted receiving $1 million from GSA for work never performed. John Rudell another contractor, admitted getting nearly as much for purportedly installing enough floor tile at the Central Intelligence Agency to cover a building six times its size.

Substantial portions of the money were then kicked back to the GSA officials who approved the bogus work. Elmer A. Van Pelt, the GSA employe who approved the work at the CIA, got a house built to his specifications.