PRESIDENTS HAVE BEEN complaining about the legislative veto for years now - but President Carter has finally done something about it. He told Congress last month that he regards the devices as unconstitutional and will not consider himself legally bound by any veto resolutions. The House of Representatives promptly responded - after a flurry of anti-bureaucratic oratory - by adding just such a veto clause to the HUD authorization bill. Thus the stage is set for a great struggle, probably in the courts, between two branches of government.

The legislative veto was invented to shortcut the legislative process. By means of it, Congress asserts that either house, or a specific committee, can kill new rules or regulations of an executive branch department or agency simply by passing a resolution of disapproval. To accomplish that, Congress requires that certain kinds of rules be submitted to it 30 or 60 days before they go into effect so that it can veto them if it wants to.

Supporters of this mechanism contend Congress needs it to keep the bureaucracy under control. They argue that without this check government agencies can issue regulations that distort or reverse the intent of Congress, and get away with it. That's so, they say, because passing a law to overturn those regulations would be time-consuming and difficult, since the president might veto the law, leaving the regulations in effect. "The question is, who makes the laws of the United States?" Rep. Elliot H. Levitas (D-Ga.) asked on the House floor the other day. "Is it the elected members of Congress or the unelected bureaucracy?"

The argument has a superficial appeal, but it evades the real issues. One of those is whether Congress delegates too much power to the bureaucracy in the first place. The other is whether Congress, having once given up such delegated power, can follow it across the gap to the executive branch and supervise how it is used.

The truth is that Congress wouldn't need a legislative veto if it wrote detailed laws - which it formerly did. It wants the veto for situations that usually concern complex or controversial subjects and in which it has written a broadly worded law and left to the bureaucracy the job of filling in the details or writing the rules. The president's argument is that Congress cannot move into the executive branch as a supervisor. That, he says, is his job.

The irony of this conflict is that it grows directly out of the last big quarrel over the power of Congress to delegate. Congress won that one - and the right to delegate extensively - in the 1930s after a bruising battle with the Supreme Court. Decades later, it began to recognize tha danger of its victory. By seeking a back-door method of controlling the authority it has giiven away, Congress is almost conceding that it has delegated too much. It can get that authority back by writing more detailed laws or overriding by legislation the rules and regulations it dislikes. It should not get it back by intruding into the day-to-day operations of the executive branch.