On the morrow of landslide, the winner traditionally receives only cheers. But Ronald Reagan is now into something deep and heavy. So it seems more appropriate to describe the challenge ahead, and the kind of help he requires. Reagan will come to the White House with less knowledge of Washington and the world than any previous president in the past half-century. He is further distinguished by belief in a conservative approach to government that has never been applied in practice and that many consider unworkable.

For both reasons, the president-elect needs to have associates of the highest quality. Circumstances reinforce that requirement. The country does not confront a single, overwhelming emergency that unites all Americans. Rather, there is a series of adverse trends that comes to the surface in a set of intractable problems. The problems are all the harder to resolve because the nature of their interconnection is so obscure.

The economy is on the edge of a new bout of inflation apt to abort recovery -- perhaps for a long time. The war between Iran and Iraq foreshadows further energy pinches. To the danger of conflagration in the Middle East there is added the peril that goes with an aging regime in Moscow working under pressure for a potentially explosive situation in Poland.

Merely coping with these difficulties takes some doing. Far more is required if a Reagan administration is to turn the adverse tides and organize a coherent strategy for taking control of events. To that end, a minimal condition is putting the right persons in three critical posts.

Chief of staff in the Reagan White House is most important by far, for the Reagan chief of staff will be deputy president. His basic task will be to help the president for the next four years devise a coherent strategy that embraces all of the country's major problems.

That anybody should be qualified for such a task is a semi-miracle. But as it happens, there is a person of the broad experience, high intellectual candlepower and absolute probity. He is George Shultz, secretary of labor and the Treasury in the Nixon administration, formerly a professor at the University of Chicago and most recently a high executive in an international construction company. Shultz blends domestic and foreign experience as very few people, and he has ties to labor, the academic world and the Democratic heavies in Congress. He is so well suited to be White House chief of staff that any other post -- including secretary of state -- would be a waste.

State, to be sure, is a second critical post. The new secretary will have to hit the ground running on current problems, and also establish (where none now exists) a method for developing and applying a global strategy. Former secretary Henry Kissinger -- renowned, articulate and with a strong sense of power priorities -- meets all the requirements. Through anathema to the Republican right, he could easily win Senate confirmation. In the process, Reagan would forge a foreign policy majority and show his right wing that he was boss.

Others besides Kissinger come to mind -- Alexander Haig, the former NATO commander; Donald H. Rumsfeld, former secretary of defense; William Simon and John Connally, two former secretaries of the Treasury, and William Casey, Reagan's campaign manager and former undersecretary of state. But none of them would be able to take in hand the whole foreign policy establishment with an eye toward bringing out of the current chaos a process for making coherent decisions.

Secretary of the Treasury is the third key post. Treasury has become the vantage point for coordinating economic policy across the board. The secretary leads the way for other Cabinet officers with economic responsibilites, and for such presidential aides as the director of the Office of Management and Budget and the chairman of the Council of Economic Advisers.

Fortunately, Reagan has available a wide range of choice in the economic area. Walter Wriston of the City Bank is one obvious candidate. Another is Alan Greenspan, the former CEA chairman. Probably particular attention should be paid to former secretary John Connally -- the one prominent Republican not idealogically paralyzed on the central problem of inflation. A third is former undersecretary Charls Walker.

Edwin Meese, Reagan's campaign chief of staff, said recently that he expected the main choices to be made "by Thanksgiving." In other words, we should know in the next few weeks whether, under President Reagan, this country will find a way to end the floundering of the past seven years.