A majority of the American people say they believe Jimmy Carter has done a poor job fighting inflation, but strikingly a great many do not seem to hold that against him.

The reason, according to a new national Washington Post poll, is that a large segment of the population believes that there is not much that any president can do about inflation.

And, far from being disgruntled with Carter, two years after his election the public is giving him comparatively high job ratings. He is at a level with that achieved in mid-September after the glowing success of the Camp David summit meetings, and he does as well as other recent presidents at similar points in their terms.

Carter still trails Sen. Edward M. Kennedy (D-Mass.) as the favorite among Democrats for the party's presidential nomination in 1980. But among Democrats who feel that a president can't do much to fight inflation, Carter bests Kennedy.

These findings and several others in the Post poll suggest that Americans may be undergoing a striking change in the way they view national leadership.

Traditionally, politicians and political scientists have held that the American people demand that their president be a strong figure, one who projects an image of being able to accomplish whatever he puts his mind to.

In the Post poll, half those interviewed seem to still hold to that view. But the other half may not.

If such a split has occurred, it could be of keen importance for Carter - and of perhaps more importance in the years to come. Lowered expectations of a president's ability to fight inflation could buy time for Carter, allowing him to remain politically strong even if his current drive against the high cost of living should sputter.

And while the poll cannot show it, it may be that people's expectations of what a president can do about matters other than inflation are lowered as well - and that could effect sharp changes in the nation's political dialogue.

The Post poll was conducted in the days before and immediately after Carter's Oct. 24 televised address to the nation, in which he announced a series of steps, including voluntary wage and price guidelines, aimed at attacking inflation.

In introducing the program, Carter repeatedly strove to keep people's expectations down. He said, "I do not have all the answers" and noted that "we've tried to control it, but we have not been successful." He maintained that "government cannot do the job alone," and said that, even with public support, "I cannot guarantee that our joint effort will succeed."