Members of Congress, who have not had a pay raise since the $12,900 increase they got last February, are due for a new salary adjustment this October.

By law, the lawmakers are scheduled to get whatever percentage increase goes to white collar federal workers and military personnel.

President Carter's new budget anticipates a 6.5 per cent increase, sets aside funds to pay for a 6 per cent raise while the president makes it clear he wants the increase to be 5.9 per cent, or less.

The problem for Congress is that 1978 is an election year. And Congress traditionally backs off from pay raises in election years on the fairly solid assumption that the voters get irritated by such things.

Thousands of federal career and political executives have a stake in whether Congress takes the October increases. They are the people whose pay is frozen at the $47,500 level even though government pay charts say they should be earning anywhere from $48,000 to $58,245 for Grade 18.

If Congress takes the October pay raise, whatever the amount, federal supergraders and political executives also will move up. But if Congress refuses the increase, as seems likely, the supergraders could remain frozen while their subordinates get more money. The congressional salary of 657,500 acts as a lid on top career federal pay, maintaining a $10,000 differential between the elected and the appointed.

Congress could, if it chose, deny itself the October pay raise and permit federal executives to move up anyhow. But that isn't likely since it would put some "bureaucrats" above the salary rates for members of Congress, something members of Congress don't like to do.

Half a dozen members of Congress are planning to fight any increase this year, out of either conviction or for political reasons. If they make a major issue of it, the House almost certainly would kill a raise for itself. All members, except the 30 or more who have announced plans to retire, are up for reelection this year. In the Senate, one third of the members are up for reelection.