A major federal employe union is urging the government's 2.6 million workers not to buy jogging shoes, hardware or steak dinners from the 1,200 outlets in 41 states owned by W.R. Grace & Co. until board chairman J. Peter Grace calls off his campaign to slash civil service pay and pensions.

A boycott by a major portion of the Washington area's 500,000 federal workers and retirees could put a dent in the operations of many Grace firms here.

Last year the Grace Commission, a private sector group chaired by Grace, recommended major federal spending cuts. It was especially critical of what it said are overly generous salaries, retirement benefits and leave for U.S. workers. President Reagan incorporated many of the recommendations in his budget. Many are expected to be sent to Congress this year.

Federal and postal unions and retiree groups say that much of the data presented by the Grace Commission are inaccurate or misleading. They cite reports by the General Accounting Office and private management firms that said pension benefits offered by W.R. Grace & Co., which include optional tax-deferred investment programs, are better than those provided by the government.

Two weeks ago the 60,000-member National Treasury Employees Union got 200 of its staff and members here to picket the Devon Bar & Grill, a Grace outlet near the White House. Picketers carried signs urging patrons, many of whom were federal workers, to dine elsewhere. Several other federal and postal unions affiliated with the AFL-CIO (the NTEU is independent) are considering joining the boycott.

The union will have a full-page ad Monday in the Federal Times, a popular weekly newspaper aimed at federal employes, asking all government employes to boycott Grace firms until the chairman "apologizes" to civil servants. A spokesman at Grace headquarters in New York said Friday that the corporation was not aware of the boycott and would withhold comment until it studied the situation. Grace was in Washington Friday making a speech urging the government to adopt his commission's budget-cutting recommendations.

The union also is asking members to sign cards pledging not to shop at Grace outlets. Locally, Grace Co. outlets include Herman's Sporting Goods stores, the Devon Bar & Grill, Houlihan's Old Place, and Channel Home Centers.

The NTEU said that picketing at some Grace operations will resume here this week and is scheduled also in Hartford, San Francisco, Austin, Chicago, Denver and Atlanta. A Grace outlet was picketed in Boston two weeks ago, a union spokesman said.

If the boycott spreads, it would be the first time that federal workers have flexed their financial muscle. The typical civil servant in the Washington area earns around $30,000. Federal employes are forbidden to strike (remember the air traffic controllers?) and their wages and fringe benefits are established by Congress and the White House.

Most congressional leaders have rejected the idea of a 5 percent pay cut proposed by Reagan, either because they don't think it is fair or because of the economic impact it would have on their communities. The federal payroll, now in excess of $900 million a month, is a major factor in the economic health of Washington -- and of local merchants.

NTEU President Robert Tobias said the boycott is "not only directed at the man Grace , but also at the Reagan administration."

"We demand an apology from that man," Tobias said, for "presenting a false picture of federal employes while moving them into exile status."