THE PRESIDENT is, by all reports, a good-natured man. But now and then he gets fed up. Yesterday he told Sen. Bob Dole that, once again, he had "had it up to his keister." This time the objects of the president's ire were not indiscreet White House aides, but the nation's bankers. The bankers had succeeded--temporarily--in stalling the Social Security rescue measure in yet another attempt to repeal withholding of taxes on interest and dividends.

The president's display of temper--said by an aide to be "probably the best yet"--was well justified. The withholding issue is important in its own right because it is a sensible and necessary step toward making the tax system fairer and more efficient. It will, no doubt, cause some expense for the banks--though, as Treasury Secretary Regan recently noted, far less than they claim. And it will cause some inconvenience for their customers-- especially those who have been neglecting to pay the taxes they owe. But these are small prices to pay for ensuring the integrity of our tax system and reducing the need for higher taxes in other forms.

The shenanigans in the Senate over the withholding issue are worrisome on still larger grounds. You will note that the House managed to pass both the emergency jobs bill and the still more controversial and important Social Security measure without kowtowing to the banking lobby. That's because its members, knowing well their own collective propensity for chaos, impose strict rules on debate on important measures, thus shielding the members from the importuning of well-heeled lobbies.

The Senate, however, has traditionally held itself in higher regard. It allows its deliberations to be conducted under various sorts of "gentlemen's agreements." That procedure held up remarkably well under last year's difficult budget and tax debates. Some senators, however, seem to have remembered that if there is one thing that gentlemen don't know how to deal with effectively, it is a child throwing a tantrum. They have learned that if they just yell loud enough or hold their breath and threaten to turn blue, sooner or later the gentlemen will give them what they want--if only to shut them up and return to polite conversation.

This is not a lesson that will be lost on the numerous special interests who roam the halls of Congress jingling change in their pockets. The best thing that these lobbyists can hope for is to persuade a member to tack their special favor on to a piece of legislation that, because it is so clearly in the national interest, is essentially veto-proof. With the Senate playing this kind of game on important measures, neither the president nor the Senate leadership will find it easy to keep either tempers or legislation under control.