Walter Mondale's face shines from the front cover of both Time and Newsweek this week, so I guess the nomination part of the presidential campaign is about over. As to the bigger issue, it seems generally felt in Washington that Mr. Reagan has the political edge at the moment, but it is almost always immediately added that there are many imponderables as to what kind of a campaigner Mondale will make. Who will he pick for running mate? Can Mr. Reagan do something about arms control - the world is waiting. How about the economy?
At home, on the surface things look favorable for the Republicans. Unemployment is down. Mr. Reagan emphasizes the positive. But there are anxieties, and they're surfacing at his press conference. Why are interest rates so high? Can the world absorb its enormous load of debt? Why does the stock market decline?
Questions like this have been answered optimistically at a hearing before the congressional Joint Economic Committee here this week, when the US Chamber of Commerce sent in a crack team including Dr. Richard Rahn, chief economist of the chamber, to support President Reagan's recent tax cuts. They denied that these aid the rich at the expense of the poor. The cuts were put into effect in the Economic Recovery Tax Act of 1981. Said Dr. Rahn: ''They have been a prime ingredient in the current economic expansion.'' Take them away? Why, that would ''threaten to reverse all the gains that have been made so far!''
The trouble is getting these tax cuts and balancing the budget, too. The situation reminded several witnesses of the happy days of Calvin Coolidge, when slight, frail Treasury Secretary Andrew Mellon was guiding things. He had a hand of steel under a gentle Edwardian formal manner and a sure confidence (shared by the nation) that - as Coolidge put it - ''This is a business country and it wants a business government.''
Andy Mellon hadn't been cited in Washington for quite a time. Sen. Roger Jepsen (R) of Iowa, chairman of the present Joint Economic Committee, cited him reverently as an advocate of lower taxes. He recalled Mellon's contention that often lower taxes actually bring in more money: ''The history of taxation shows, '' Mellon said, ''that taxes which are inherently excessive are not paid. The high rates inevitably put pressure on the taxpayer to withdraw his capital from productive business and invest it in tax-exempt securities, or to find some other lawful methods of avoiding the realization of taxable income.''
Senator Jepsen purred over that. And Prof. Richard Vedder of Ohio University joined in: Charges that the 1981 Reagan tax cuts are unfair to the poor are ''without foundation,'' he declared.
Well, Andrew Mellon was a venerated figure, who came to symbolize an epoch. The difficulty is to fit him in to the present. He also backed a balanced budget. What would he say to a $200 billion annual Treasury deficit? He was a man of absolutes.
The world looks anxiously at the American recovery. Will it last? What is going on, anyway? Uneasiness has even reached the stock market. Government deficits have created a demand for money that has stretched interest rates to a worrisome height. The American dollar is quite high in relation to other currencies. As the careful London Economist points out, ''The country's visible trade deficit, over $21 billion in April alone, is so far running at almost double last year's level of $69 billion. Demands for tariff protection are breaking out.''
That's the complex picture. Powerful forces are stirring in the world. It made me nostalgic to hear Andy Mellon invoked this week. But it brought a shiver , too.