The annual multimillion- dollar federal pay raise game between Congress and the White House begins next month with both sides, as usual, understandably confused about its complex rules.

Caught in the middle, as usual, are more than 2 million white-collar civil servants, including more than 350,000 in the Washington-Baltimore area. Equally interested parties are the government's half-million carpenters, electricians and other skilled craft, or blue- collar, employes who are technically under a different set of rules but who usually wind up getting the same percentage increases in pay raises as white- collar employes. The magic figure for January is probably 3 percent, or a little more.

If President Reagan sticks with his original budget plan, he will recommend next month a January 1988 raise of 2 percent for white-collar civilian federal workers and 4 percent for military personnel.

This year federal workers got a 3 percent raise; last year they got no increase.

Congress is expected to recommend a minimum 3 percent civilian federal pay raise -- and that could be increased to 3 1/2 or even 4 percent -- for January, with follow-up 3 percent raises in January 1989 and 1990.

The primary reason federal pay rules are so confusing is that they are used only once a year, and rarely work out as intended. For example:

By law U.S. workers are supposed to get a pay adjustment each October to bring their salaries up to "comparability" with similar jobs in the private sector. That much-disputed comparability figure is based on private sector pay data collected by the Bureau of Labor Statistics and then massaged and interpreted by various official panels and agents acting for the president. In recent years the raw pay data have shown that government pay, on average, is 20 percent behind the private sector. The pay law says the president must propose an alternative to that catchup figure by Sept. 1 or it automatically goes into effect in October.

Typically presidents recommend smaller raises delayed until January. Congress, faced with the choice of accepting that or rejecting it with the alternative being much larger raises, usually goes along. Because each percentage point of federal pay raise costs between $500 million and $800 million, depending on who does the estimates, even small increases have major budgetary and political implications.

This year Congress appears to have found a way to guarantee federal workers a raise without going along with the unacceptable alternative of granting 20 percent-plus catchups. The budget reconciliation bill would, if approved, set raises for the next three years that would overrule any lesser increase proposed by the president.

Although none of this is over, as the coach says, until it's over, chances are that civil servants will get a raise of 3 percent (or slightly more) in January.Longtimers

Roy H. Rose, a visual presentation officer, has retired from the FBI. Rose joined the bureau in 1943 and was considered one of the nation's experts in demonstrative evidence techniques. Also retiring is printing specialist Margie C. Elmore, who came on duty in 1942. Pension Shopping

The current issue of the newspaper published by Federally Employed Women Inc. includes an excellent analysis of the old and new federal retirement programs. Government workers hired before 1984 must decide whether to switch to the new Federal Employees Retirement System, or stick with their current Civil Service Retirement System.