Jimmy Carter is "in severe danger of not being renominated for the presidency," Ronald Reagan's campaign manager said yesterday.

John Sears, Reagan's top political strategist, said Carter is vulnerable not only to Sen. Edward Kennedy (D-Mass.), the favorite of many dissident Democrats, but to a host of other potential candidates, including California Gov. Edmund G. Brown Jr.

"I've heard people say Carter is actually a political hemophiliac. Once scratched he'll probably bleed to death," he told a breakfast meeting of reporters."I tend to agree with that."

Carter, he said, "is the weakest incumbent president in this century."

Coming from the campaign manager for the front-runner for the GOP nomination, Sear's assessment is not without severa bias. But it symbolic of a growing feeling in the political community about the weaknesses of the president-weaknesses that Republican strategists must take into account as they plot out their plans for 1980. One GOP hopeful, former Texas governor John Connally, has long taken a similar position, stating he feels Kennedy will be the nominee.

Sears went considerably further in speculating about Carter's Democratic Party than Reagan has himself. In a cross-country tour this week, the former California governor appeared uncertain when asked about Carter's political strength, as if he were still weighing the matter in his mind.

Reagan has yet to make a formal announcement of his candidacy for the Republican nomination, and doesn't plan to do so until the fall. But he has a campaign committee working in his behalf and is traveling about the country speaking to various political and business groups.

On other subjects, Sears groups.

On other subjects, Sears said:

Reagan's position as GOP frontrunner is different from that of other candidates in the past, such as Sen. Edmund Muskie (D-Maine) in 1972 and former Michigan Republican governor George Romney in 1968. "All they had really going for them was a lead in the polls," he said. "What we have is a group of people who've been through if before. We have solid rock-bottom support."

Polls made for the Reagan campaign, unlike those made by others, indicate Reagan's age is not a problem. He is 67.