Washington — It's the second-most-important election of the year, and yet there are no pollsters, no public campaign speeches, and no bumper stickers. In fact, the race for majority leader of the United States Senate will be over in just 10 days, and no one can reliably predict its outcome.
Conducted in the privacy of senatorial chambers and by telephone calls to vacationing colleagues, the campaign appears to have reached a stalemate, with all five contestants having about the same number of supporters. But even the candidates cannot be certain, since the balloting Nov. 28 will be secret.
So obscure and complex are the issues in the majority leader race that the current big factor is not the candidates themselves, but whether Sen. Jesse Helms will take over as chairman of the Senate Foreign Relations Committee.
The North Carolinian, who is also leader of the far-right wing of the Republican Party, announced last week that ''it is my intent'' to remain as chairman of the Senate Agriculture Committee, although he has the seniority to switch to the prestigious Senate Foreign Relations Committee. (The committee had been headed by Sen. Charles Percy of Illinois, who was defeated for reelection on Nov. 6.)
Senator Helms's promise, far from unequivocal, touched off a new round of speculation in the senatorial offices on Capitol Hill.
One theory is that it will boost Sen. Richard G. Lugar of Indiana, who is next in line for the foreign relations chairmanship after Helms. If Senator Lugar, a conservative, were to become Senate majority leader (replacing the retiring Sen. Howard Baker of Tennessee), that would leave the foreign relations panel in the hands of a Republican liberal, Sen. Charles McC. Mathias Jr. of Maryland.
At that point, goes the theory, Senator Helms could consult with President Reagan and then announce that for the good of the nation he must become foreign relations chairman. Farmers back in North Carolina are already prepared for the move.
''I believe that our members would understand if the senator were to switch, '' says W. B. Jenkins, a spokesman for the North Carolina Farm Bureau.
Moreover, if Lugar is chosen leader, he would not take over the Senate Agriculture Committee, where he ranks just behind Helms. Lugar opposes tobacco programs, but the next senator in line, Thad Cochran of Mississippi, is considered to be a friend of crop price-support programs.
Of course, senators who are wary of putting the doctrinaire and unpredictable Helms in charge of the Foreign Relations Committee might vote against Lugar just to block Helms.
If that reasoning is convoluted, it is only one side of the Rubik's Cube puzzle that the Senate majority leader's race has become.
Based on demonstrated legislative skills and national stature, GOP Sen. Robert Dole of Kansas has long been seen as a front-runner. But the chairman of the Senate Finance Committee has presidential ambitions for '88.
Also, if he is elected, then Sen. Bob Packwood of Oregon takes over the Finance Committee, and Senator Packwood has had tiffs with the Reagan White House.
Sen. Ted Stevens of Alaska, now No. 2 in the Republican leadership, had been counted out of the race but has now moved into the pack. Less outspoken on political philosophy than many senators, he's running on an ''experience counts'' platform.
Sen. James A. McClure of Idaho has tried to move away from his slot as the ''conservatives' candidate'' to pick up more backers. He and Lugar are both hugging close to the Reagan administration.
But Senator McClure is competing for Western senators with Sen. Pete V. Domenici of New Mexico, a moderate who has run the most low-keyed campaign of the five.