Congressional budget choppers, once confident they could get the Senate and House to take federal and military retirees (100,000 here) off their enriched diet of two cost-of-living adjustments (COLAs) per year, may again be outfoxed by the politically tough gray power lobby. The billion-dollar COLA issue will be decided in a couple of weeks by Senate-House budget conferees.

The Senate's budget reconciliation bill is almost certain to have Reagan administration-approved language that would limit U.S. retirees, who now get inflation catch-ups each March and September, to a single annual raise, with the next COLA withheld until March 1982.

On the House side, the Post Office-Civil Service Committee has proposed a budget compromise -- a pay-pension offset for 175,000 military retirees now working as civil servants -- as a substitute for the COLA cutback suggested by the Budget Committee, which wants to trim retirement program spending.

The House Rules Committee next week will consider requests from members who would like to amend the budget reconciliation package. One of those amendments would limit retirees to one raise each March.

If the Rules Committee refuses to allow such an amendment, odds are good that the House will approve a budget-cutting package that leaves the twice yearly COLA raises intact.

Then it would be up to the Joint Conference Committee (composed of Senate and House members) to reach agreement on a budget package, and decide whether to make savings in federal retirement programs by cutting out one of the COLAs, or by reducing civil service salaries of military retirees by the amount of their military pensions.

Federal and postal unions are working on Rules Committee members, asking them not to allow any amendment that would endanger one of the cost-of-living raises. The giant National Association of Retired Federal Employees is contacting its 300,000-plus members, asking them to urge senators and representatives to spare the raises.

Retirees hold the balance of voter power in many districts, particularly in Sun Belt areas that are strongly Republican.