SUPPOSE that while in Tirana, Albania, recently, the secretary of state was called to the phone. President Bush, in Washington, asked his old friend how things were going and then added, "What should I do about John Sununu?"This is an imaginary scenario. Yet it may well have happened, since Jim Baker is the person the president relies upon more than anyone else when he faces a big problem. Mr. Bush spent long hours with Mr. Baker thinking through the crisis in the Persian Gulf; those conversations shaped the US response to that crisis and the rationale for the response. That, of course, was a subject that a secretary of state would normally have been consulted about - particularly a secretary who had been so active as Bush's emissary to the Middle East and to the United Nations. But Bush relies on Baker's judgment across the board, on domestic matters as well as foreign affairs and on a wi de variety of political and policy decisions. This relationship is long standing. These two Texans are buddies. Bush respects and likes no one in public life more than Jim Baker. Accordingly, the president not only elevated Baker to the No. 1 spot in the Cabinet, but he also is known to have asked for and received Baker's advice on other major appointments, including that of John Sununu as White House chief of staff. Mr. Sununu is there because of the president's gratitude for the former New Hampshire governor's help in shaping a vital Bush victory in the 1988 primary in that state. But Bush wanted the judgment of Baker, who had been chief of staff and treasury secretary under Ronald Reagan, on whether Sununu would be the right person to sit at his right hand. Baker thought "yes at the time. Sununu, who says he is determined to stay on, may weather the storm caused by his controversial travel habits. He has apologized. If he now keeps a lower profile, he may save his job. But Sununu's travel improprieties merely brought into the open a growing antipathy for him among some of Bush's top people. They think that Sununu has been throwing his weight around too much, that he's acting as though he were assistant president. Where's Baker in all this? There have been no public utterances from the secretary of state, who has been spending much of his time abroad. But at a gathering of politicians and the press not long ago, he poked fun at Sununu for always standing close to the president in order to get into the photos being taken. As he made these comments, Baker wore a slight smile. But it was clear, I thought, that he was sending a message to the president, sitting close by: Sununu was getting a little big for his britche s. Sununu is sometimes spoken of as the "real head" of the Republican Party. The sitting president, not the party chairman, holds the party's political power. So Sununu, as the president's right-hand man, can speak and act with much authority on political matters. But, again, the person Bush habitually turns for advice on the biggest party and campaign decisions is Baker. For example, as the next campaign rolls around he will call Baker - no matter if he's in Washington, Israel, Jordan, Russia, or anywhere - for advice on whether to debate his Democratic opponent and, if so, how many debates there should be. Baker has been recognized as a canny advisory on debates since the days when he and others urged President Ford to use his speech at the 1976 GOP national convention as an occasion to challenge Jimmy Carter to a debate. And it was Baker who twice shaped the debate strategy of Reagan and then of Bush in 1988. If Bush is way out in front of his opponent in the polls, as he might well be, don't rule out the possibility that Bush - with Baker's advice - will not debate at all in 1992. That is, he'll do to hi s opponent what Nixon did to McGovern in 1968. Bush may conduct a campaign from the White House Rose Garden, venturing out once in a while to help some candidate but not waging an all-out campaign around the country. The president will talk to Baker about that, and Baker's advice will carry more weight than that of anyone else.