The Labor Department says it may have to fire as many as 2,460 of its 21,000 workers over the next few months to comply with a 12 percent spending cut the Reagan administration has ordered for nondefense operations of government during this fiscal year.

Labor's action, in the form of an official alert to American Federation of Government Employees units representing field and headquarters staffers, is the forerunner of RIF (reduction in force) warnings that will be coming to workers in most other federal agencies over the next few weeks.

Department brass say the 2,460 number represents the cutbacks Labor would have to make if it has to take the 12 percent cuts from its personnel operations. Those reductions will be in addition to lower personnel ceilings that Labor and other nondefense agencies will be assigned over the next two years.

Officials say they have no idea how many people will actually be RIFfed, or how many of the cuts will have to be made from its Washington staff of 7,600. The size of the actual cuts will depend on a battle shaping up in Congress to determine if the administration can impose a spending cut if the Senate and House vote the same or higher level appropriations for various departments and agencies.

On Oct. 6 this column reported that because of the double-barrel personnel and fund cuts in the works ". . . nondefense agencies may be forced to cut as many as 150,000 jobs, with some heavy layoffs coming as early as this Christmas, over the next two years . . . ."

The Labor Department got out the early warning because its contracts with the American Federation of Government Employees requires it to give 120 days' notice of major cutbacks. Officials say that RIFs could come before that time, but the union must be notified.

The estimate of a 150,000-job cutback is based on previously announced administration plans to trim 75,000 jobs in most agencies over the next two years, plus the possibility that another 75,000 jobs could be eliminated if the 12 percent spending cuts hold up -- Congress will fight some of them -- and if those cuts are made primarily in salary funds.

Other agencies will be getting forecasts of possibly severe RIF actions in the next few weeks although the actual number of people fired will be determined by congressional action, and how much of the cuts must be made in personnel rather than program.