The first hours disclosed the basic features of the Reagan second term. President Reagan is going for the chance to make history by securing an arms control accord with Russia and a reform of the tax system.

Dividing the right wing, the better to make arms control possible, turns out to be much easier than previously supposed. But it remains a puzzle as to how Reagan and his new chief of staff, Donald Regan, can line up support within the administration and Congress for a responsible fiscal policy.

The best sign of purpose comes from the Inaugural Address. From amidst the rhetorical splendor and the paean of praise for the "American sound," there emerged an emphasis on arms reduction, fiscal responsibility and tax reform.

The great obstacle to arms control figure to be the Pentagon hawks. A military man, Gen. Edward Rowny, had played a key part in gumming up the START negotiations on long-range missiles. As head of the negotiating team in Geneva, Rowny was out front for the anti-arms-control cabal in the Pentagon. His backers included Secretary Caspar Weinberger, Assistant Secretary Richard Perle and some of the uniformed military.

At the recent Geneva meeting between Secretary of State George Shultz and Foreign Minister Andrei Gromyko, Rowny struck one of the few sour notes. He forced his way into photos and expressed doubts about the part of the communique which identified as one purpose of the talks "preventing an arms race in space." Getting an accord with Rowny as a negotiator shaped up as impossible.

So a little bit of surgery was neatly accomplished. Max Kampelman, a Democrat closely associated with Hubert Humphrey, was named to head the umbrella group that will handle all arms control talks with the Russians. Former senator John Tower of Texas -- who had been up for consideration as ambassador to West Germany -- was persuaded by Secretary Shultz to replace Rowny as head of that part of the delegation dealing with long-range missiles.

Both newcomers represent significant parts of the right-wing coalition in foreign policy. Kampelman has strong credentials with the pro-Israeli hawks who have figured as a source of ideas for the New Right. Tower represents the southern conservatives in the Senate who have always laid stress on American military power. While neither man is an arms control enthusiast, both have the common sense to want an agreement that codifies rough parity at a lower level. Thus the committed anti- arms-control faction in the country has been cut to a handful of die-hards.

As to fiscal affairs, James Baker, the White House chief of staff who has been named secretary of the Treasury, is in a strong position to do that job. He has broad experience in dealing with Congress and various segments of American business. He will be a distinct asset in mobilizing Republican and Democratic support for programs to reduce the deficit and reform taxes.

To be sure, he lacks experience in international finance. But no one should suppose that the outgoing secretary, Don Regan, knew his way around that arcane subject. Over the past four years the United States counted for a cipher in international financial affairs. The serious business has been done by Paul Volcker, chairman of the Federal Reserve Board, and Jacques de Larosiere of the International Monetary Fund. They will probably continue as the dominant figures. It should be noted in that respect that Volcker was invited to the second inaugural, whereas he had not been asked to the ceremonies in 1981.

The hard part is going to be lining up the administration and Congress for an early move to close budget deficits. For the administration has put together a package which feates cuts in domestic spending. The Senate Republicans want to append cuts that go much deeper into defense spending. The thought is that if Republicans push a budget through the Senate in the next couple of months, they can then divide the House Democrats on a single up-or-down vote on the issue of government spending.

Chances for that strategy's working have never been better than 50-50. They recede as the days pass. Budget Director David Stockman and Senate Majority Leader Robert Dole keep changing elements of the package. Meanwhile the Democrats hang back, asserting there can be no serious cuts in domestic spending without roughly parallel cuts in defense outlays.

Putting all these pieces together will devolve mainly on the incoming White House chief of staff, Treasury Secretary Don Regan. Regan clearly is simpatico with the president. No one should take seriously his modest disclaimers about not being political. Few men are more so.

What Regan has not demonstrated is that he can move deftly from ne subject to the next -- one day a filibuster, the next day arms control, the next day school prayer, and the day after that trade with Japan. His reputation as a good manager with a knack for delegation is the reverse of reassuring. For the essence of reasoning with a senator who wants to filibuster is that you can't delegate the job.

So the outcome of the Reagan years remains a puzzle. The one sure thing is that the longer matters drag, the harder it will be to realize the president's historic goals.