Senate Majority Leader Robert J. Dole (R- Kan.) is a man who feasts on challenges; 1986 will bring him enough to satisfy even his appetite. Sitting in his office a few days ago, Dole ticked off the things that have to fall into place for this to be a happy new year for him and his party:

*The Senate must pass the tax-revision bill that President Reagan put at the top of his second-term domestic agenda and pushed through the House in December with a last-minute lobbying blitz.

The Senate must demonstrate that it can use the Gramm-Rudman-Hollings budget process, which it invented out of desperation late in 1985, to produce meaningful deficit reductions.

*The Senate must deal with another pinching economic problem by passing a trade bill that helps prevent predatory export practices by other nations and opens foreign markets to U.S. goods and services. It may also have to revisit farm legislation if, as seems likely, the 1985 agriculture bill fails to alleviate acute distress in rural America.

*The majority leader must win his own re- election race in Kansas (which seems well in hand) and lend his assistance to other Republican senators, in order to hold the shaky 53-47 Republican majority in a year when the GOP must defend almost twice as many Senate seats as the Democrats.

If Dole can do those four or five big things, then he may, just may, have an entering wedge for the 1988 GOP presidential race, which he longs to contest. Otherwise, forget it.

Dole is not daunted. At 62, he has a passion for power that all his wisecracks and joking cannot conceal. Luckily for the Senate and the nation, it is linked to a subtle mind and an instinct for governing as acute as the Senate has seen since the days of Lyndon B. Johnson.

Most of his colleagues say Dole did very well in his first year as the successor to retired majority leader Howard H. Baker Jr. But this year will be tougher. Dole will have to find a way to mesh the election needs of his diverse Republican colleagues with the different priorities of the Democratic House. Toughest of all, he will have to craft the tax, trade and budget bills to meet the standards Reagan has set out, or persuade Reagan to back down, or take the risk of putting the Republican Senate in conflict with a venerated Republican president in an election year.

Conflicts threaten everywhere. On taxes, for example, Dole said: "We have to have a bipartisan bill to get it through the Senate. . . . I think we can pass one, but it won't necessarily be what the president prescribes." Reagan squeezed a tax bill through the House last month only by promising Republicans there he would veto any measure that did not meet the major conditions set by such people as Rep. Jack Kemp (R-N.Y.), possibly Dole's least favorite colleague.

Dole told me, "If you do all the things he (Reagan) promised Kemp, the first question is how do you pay for them?" Somebody, he suggests, will have to bend.

The dilemma is even sharper on deficit reduction. Dole embraced Gramm-Rudman but said, "I fault them for taking Social Security off the list" for savings. As for the president, Dole said, "If he insists that defense, Social Security and interest payments are all sacred and taxes can't be raised, I just don't think we'll be able to get the deficits on the downward glide path Gramm-Rudman sets." Again, someone will have to bend.

At some point this spring or summer, Dole said, "it will be hard to avoid" merging consideration of tax reform and the budget. "When that day comes, it will impose some hard choices on the White House."

What I understand Dole to be saying is that the president will have to back off his flat opposition to any kind of tax increase and accept what Dole has long regarded as inevitable: the need for new revenues. "There will be no effort up here at revenue enhancement without the White House's approval," he said pointedly.

Fresh fights are possible also on trade and farm legislation, where Reagan in 1985 imposed one veto and threatened another in order to enforce his budgetary and economic theories. Dole does not blanch at the prospect of a showdown with Reagan or the administration heavyweights. Last year, he publicly challenged Treasury Secretary James A. Baker III on the timing of tax reform; Secretary of Defense Caspar W. Weinberger on military spending; Attorney General Edwin Meese III on voting-rights enforcement; and White House Chief of Staff Donald T. Regan on his handling of Congress.

But in this election year, with control of the Senate in doubt and his campaigning colleagues counting on him to protect their interests, the risks of a fight with the White House go well beyond Dole's own future ambitions.

"The president is the best asset we've got," Dole said, but then characteristically asserted his own power. "I don't think I've initiated one phone call to the White House all year," he said. "They call me."

"They" will be calling often in 1986. And what he answers may well be the central and decisive story in this fascinating political-governmental year.