Democratic presidential candidate Edward M. Kennedy says he opposes the White House plan to take away one of the two COL (cost of living) raises that federal and military retirees now get each year.

Kennedy's pledge was made yesterday to a Montgomery County federal retiree group by U.S. Rep. Barbara A. Mikulski of Baltimore, who is heading Kennedy's Maryland campaign. Kennedy's office confirmed that he favors keeping the COL adjustments that nearly 4 million U.S. retirees now get every six months -- in March and in September.

The two-COL promise is a clear-cut move to capitalize on growing disenchantment with the Carter administration by federal and postal employes, the 2.6 million civilian workers and retirees who stand to lose about $1 a day in spendable income if Congress eliminates one of the two inflation adjustments.

Mikulski told members of the National Association of Retired Federal Employes that Kennedy believes it is "unfair to change the rules in the middle of the game," and opposes any changes in retirement benefits promised to federal and postal workers.

Kennedy's promise comes at the perfect time for his campaign. There are more than 100,000 federal and military retirees in the metro Washington area, and D.C. has its primary election today. The COL is a major economic item to thousands of people here.

(Carter aides say it is easy for Kennedy to oppose the idea of a single COL raise, since the Senate and House probably will decide it before the November elections. "Watch how he [Kennedy] votes on the budget resolution when it comes up in the Senate," a Carter backer said. He said the single annual COL adjustment would be "consistent" with adjustments for social security benefits and would help balance the budget.)

Kennedy -- through Mikulski -- also took a jab at President Carter for ordering federal workers to pay for parking, and for "blaming" the bureaucracy for every problem, from inflation to troubles with the OPEC cartel.

(Carter staffers say the president's position on federal workers has been constantly misrepresented and/or misinterpreted. They say he believes the typical civil servant does outstanding work, and seeks only changes that would streamline the bureaucracy's creaky machinery.)

Kennedy and Carter have almost the same stand on the controversial issue of mandatory social security coverage for federal and postal workers. U.S. employes now have their own pension system outside of social security. Few favor "integration" of the systems, fearing it would reduce benefits or cost them much more to maintain the same level of benefits.

Both Carter and Kennedy have said they will oppose any linkup of the two systems -- social security and civil service -- if it "hurts" employes, or cuts into vested benefits. Those promises leave a lot of room for maneuvering, however, since their definitions of what hurts and what does not hurt might not tally with what federal and postal workers consider pain.

The House is scheduled today to take up recommendations of its budget committee, which include a single COL raise each year for federal and military retirees. The House plan would limit retirees to a single inflation adjustment each July. President Carter ahs proposed a single adjustment each March.