You can't beat somebody with nobody. Especially when the somebody is the president of the United States.

So for all his difficulty in running the country, Jimmy Carter remains the man to beat in 1980. Indeed, as the political season begins anew, he is the favorite for both renomination and reelection.

To be sure, there appears to be next to no enthusiasm for the president anywhere in the country. Scandal dogs some of his closest aides. He has lost the capacity to influence decisively the two forces most important in shaping the political atmosphere -- inflation and recession.

Still, Carter has finally taken a step absolutely crucial to success in the post-imperial presidency. He has lowered his sights. He can proclaim himself a winner if he gains approval of the strategic arms limitation treaty and passage of a windfall profits tax on the oil companies.

That modest program leaves Carter no sword on which to throw himself -- nothing so big to warrant abandoning the White House as Harry Truman and Lyndon Johnson did. Even the loss of a primary or two would not necessarily force Carter to self-destruct.

In the absence of a withdrawal by Carter, Edward Kennedy will probably not enter the race. Family reasons have always been one barrier to a declaration by the senator from Massachusetts. He has just come off a month with the family. Nothing indicates that the obstacle posed by the fate of his brothers and the vulnerability of his wife and children has been lowered.

Nor have the political reasons barring a direct challenge lessened. The senator would still make enemies he does not need to make, and risk spliting his own party and thus compromising his chances for 1984.

Maybe Gov. Edmund Brown of California could force him into the face. But in a contest between Carter and Brown, the president is not the underdog. So Carter emerges from the analysis as the man most likely to win the Democratic nomination.

The condition of the Republicans makes the Democratic nominations eminently worth having. Ronald Reagan is probably the most solid front-runner in an out party since Dewey in 1948. He not only has name recognition and organization, but, more important, he has working for him perhaps the best political strategist in the country -- John Sears. Sears has established himself the No. 1 adviser in the Reagan camp. Hence, the recent departure of his chief rival, Lyn Nofziger.

Thanks to Sears, Reagan has identified his weaknesses and is working to overcome them. He has put out lines toward the blue-collar section of the national electorate and into the Rockefeller wing of the Republican Party. He has avoided mistakes, and it is hard to see the Republican who can beat him for the nomination.

John Connally, the former Democratic governor of Texas, who jumped to the GOP after serving in Richard Nixon's Cabinet as secretary of the treasury, is one possibility. He has a commanding presence, which contrasts advantageously with Carter's sad-sack approach. He has strong following in the business community, and therefore plenty of money.

However, he has not moved from the board room into the hearts of Republican Party workers. That failure tends to undo his basic strategy. The original idea was that he would let Reagan forge out front in the early caucus and primary states, and then overtake him in the Southern states.

The first of the Southern states is Florida. There will be a straw poll of the state convention next month. Already some 400 of the 1,300 delegates have been chosen. According to one reliable count, Reagen has 42 percent. Connally has only 19 percent.

Howard Baker, the Senate minority leader, has the competence and experience that Carter lacks. The country thinks highly of him. He ran evenly with Carter in a recent poll by Time Inc.

Still, only half of the voters in that poll knew Baker. He is glued to the Senate, which is not the best launching pad these days. Moreover, he has taken a hard-line position on the arms limitation treaty. He will need extraordinary dexterity to come off that stance without offending Republican conservatives.

Accordingly, what is shaping up at this early stage is a Carter-Reagan struggle. As of now, the polls show Reagan ahead, another reason for thinking he'll win the nomination.

But Reagan is known to the country more as a former actor than a former governor of California. His amateur status in political life unsays the major issue against Carter -- competence. So Carter has probably a better chance of beating Reagan than any other Republican likely to win the nomination. Which is why, if you had to bet now, the favorite would be Jimmy Carter.