More than 70, 000 federal and mulitary retirees in the Washington metro area will get monthly pension checks next week reflecting a 3.9 percent before taxes cost-of-living raise.

World-wide, more than 2 million civilian and military retirees or their survivors will benefit from the raise triggered by inflation. By law, federal and military retirees get two annuity adjustments each year (March 1 and Sept. 1) to help keep them abreast with upward changes in the cost of living. The raises show up in pension checks one month after the increase goes into effect.

The twice yearly pension adjustment has been under fire from the Carter administration and private industry, where some unions are demanding the same indexing adjustment in labor contracts.

Earlier, the Carter administration floated a trial balloon, testing the winds in Congress to see what the reaction would be to legislation that would limit retirees to a single cost-of-living raise each year.

But the Defense Department argued that the change should not be made until a long-term study on military pensions is completed. In effect, the Pentagon told the White House to propose the change if it wanted, but not for military retirees. At that point, the White House decided to shelve the plan.

Now, however, key members of the Senate are looking at the pension adjustment cutback again.

If senators are convinced the idea would save money-and have political mileage-they may attach it as a rider to some other piece of legislation. While the White House isn't pushing the plan any more (White House aides say), it obviously would not stand in the way of the Senate if it decides to do what the White House wanted to do al along.