The Reagan administration's use of "informal settlement agreements" to resolve disputes between federal health and safety inspectors and employers without going to court has avoided costly litigation and led to a speedy correction of dangerous working conditions, the General Accounting Office has found.

The GAO also said the informal negotiation process used by the Occupational Safety and Health Administration is not illegal, as some critics have charged.

Since 1980, OSHA managers have been allowed to meet informally with employers to discuss penalties imposed by OSHA field inspectors. The procedure was not widely used, however, until President Reagan was elected and OSHA began trying to act less like a policeman and more like an adviser to businesses.

The GAO said the 1970 law that created OSHA neither prohibited nor allowed informal negotiations, but it said recent court decisions have upheld the agency's right to conduct them.

In most cases, OSHA supervisers met with employers after the employers objected to citations or fines levied by OSHA field inspectors. Inspectors and employes can attend the informal sessions, but few do, the GAO said.

OSHA resolved 16,736 of the 111,735 violations that field inspectors issued in 1983 through the informal settlement process. The GAO said OSHA supervisers reduced $4.1 million in fines levied in those cases to $1.8 million. In return, employers promised OSHA, either verbally or by letter, that they would fix the cited health or safety problems.

Former OSHA chief Thorne G. Auchter has contended that the informal settlements spared the government expensive and unnecessary litigation and led to the speedy correction of work-place hazards.

Critics have contended that the conferences have allowed employers to browbeat inspectors, and made inspectors reluctant to issue citations.

A spokesman for Rep. Barney Frank (D-Mass.), chairman of the House Government Operations subcommittee on manpower and housing, called the report incomplete and said the subcommittee had scheduled hearings to examine the process.

The GAO said it studied 150 settlement cases and found that OSHA supervisers had agreed to modify violations in 37 of them. In those cases, fines were reduced by an average of 56.4 percent, the GAO said. Fines frequently were reduced or eliminated without written explanation other than the employers' promise to correct a hazard, the GAO said.

The GAO criticized OSHA for not conducting adequate follow-up inspections. But the GAO said a random check showed that 86 percent of the employers had kept their promises to correct hazards.