The Government Printing Office -- which two years ago tried to cut salaries of its "overpaid" craft workers 22 percent -- is now prepared to offer them raises of up to 15 percent during the next three years, and to crack the government's 40-hour-minimum workweek barrier by putting 2,300 printers, bookbinders and production employes on a 37 1/2-hour week.

The change of heart is largely the result of a change of command at the world's largest print shop.

If the proposed contract between GPO and the unions is okayed by the Joint Congressional Committee on Printing (which is a good bet), the first raise would be effective this month. The 37 1/2-hour workweek, which would be achieved by paying employes for their lunch period, would start next June.

The contract is certain to cause a stir with other U.S. workers -- including white-collar types at GPO -- who will continue to work a 40-hour week and probably have their pay frozen next year.

The independent action by GPO, whose products range from government calendars to the Congressional Record, is possible because GPO bargains separately over wages with unions and answers to Congress rather than the White House.

President Reagan proposed a 5 percent pay cut for civil servants -- to take effect next January. But the Senate and House have instead tentatively settled on a pay freeze for 1986. If approved, that freeze would not affect the GPO craft workers because they negotiate their own contracts, although it would hit other white-collar employes at the agency.

GPO's board of directors is the Joint Committee on Printing, chaired by Sen. Charles McC. Mathias (R-Md.). Many GPO employes live in Maryland, a fact not lost on unions or GPO's top management.

The agreement was okayed by Ralph E. Kennickell Jr., who was nominated last December to head GPO. He is still awaiting confirmation from the committee headed by Mathias.

Kennickell's cooperative approach toward unions is in stark contrast to that of his predecessor, Danford Sawyer, a Florida conservative who continually butted heads with employe organizations. The blowup came when he charged that GPO's craft workers were overpaid compared to their counterparts in other government agencies or industry. He proposed a 22 percent pay cut for them but was overruled by the congressional committee, which ordered raises for workers. Sawyer is now in the private sector.

GPO compositors currently earn $16.07 per hour; bookbinders, $15.97; offset photographers, $17; plate makers, $16.62, and journeyman printing plant workers from $7.20 to $12.94 per hour, according to GPO officials. Their pay is higher than wages for most federal printers. The justifications are that GPO employs the cream of the crop and that it routinely does complex production and meets deadlines that are not expected of other agencies. It generates considerable overtime, especially when Congress goes into evening or weekend sessions.

Under the proposed contract, union-covered employes will be paid for half-hour lunch breaks each day starting next year, bringing their workweeks to 40 hours. Most other federal workers put in a 42 1/2-hour week counting lunchtime but are paid for only 40 hours.

The contract links GPO raises for the next year to the cost of living, with a "cap" of 5 percent each year. In the last two years, raises for most other civil servants have ranged between 3 1/2 percent and 4 percent.