PRESIDENT REAGAN has insisted that Congress return after the November elections for a lame-duck session. However hobbled, the lame-duck promises to be lively.

In the few short weeks before Christmas, three major conflicting interests will collide. For their part, Senate Majority Leader Howard Baker and House Speaker Tip O'Neill will be trying to control the worst impulses of a legislative body, many of whose members will not be around next year to suffer the consequences of their decisions.

The resolution calling for Congress to reconvene will surely specify that the post-election session will be limited to completing the appropriations bills as the president wants. But that's no assurance that members won't also push favorite causes, large and small. Congress might then find itself tied up considering everything from a balanced budget amendment to a measure favoring some hometown contractor. That's why the leaders resisted the lame- duck session until the president insisted on it.

The White House, however, sees a political advantage in going into the November elections waving the flag of fiscal prudence. In fact, that's not the issue at all. If Congress were simply to pass a continuing resolution to keep the government operating until next year, the control measures put into effect by the budget reconciliation process would be quite sufficient to make sure that the budget stayed within bounds. What the president is really worrying about is that the continuing resolution would give him less than he wants for defense.

The administration apparently hopes that in the extra time provided by the lame-duck session it can indulge in the veto politics that it used last year to bend Congress to its will before the Christmas recess. Under that scenario, the president would threaten to shut down the government -- or actually do it -- while his advisers worked a deal with Republican leaders in both Houses that would give him the spending combination he wants.

This year, however, the administration is likely to have a harder time. Sen. Mark Hatfield and Rep. Jamie Whitten, chairmen of the appropriations committees, support the idea of a lame-duck session because they are worried that the momentum of the budget process has eroded their control over the details of federal spending. A hastily prepared continuing resolution might also lack the details needed to allow federal agencies to operate smoothly.

But they and other leaders in both Houses are not of a mind to let the president's men ride roughshod over their concerns about the distribution of federal money. They know that they have adopted a responsible budget plan, and they intend to stick with it. The administration argues that their program cost estimates are wrong, but Congress' estimating record of recent years is a good deal better than the administration's.

The outcome of the lame-duck session will, no doubt, depend on the impact of the November elections on the legislators' frame of mind. Whatever happens, remember that the issue at stake is not "budget-busting" or irresponsible government. The fight is over how much money should be spent on domestic programs and how much should be spent on defense -- and that's a battle that's likely to continue to be fought when the new Congress convenes in January.