Sen. Edward M. Kennedy (D-Mass.) would strip President Carter of nearly all his support among Hispanics if he becomes a 1980 presidential candidate national Hispanic leaders said yesterday.

"Obviously, if Kennedy declares his candidacy, there would be a wholesale jump by Hispanic voters into the Kennedy camp," said Ruben Bonilla, president of the League of United Latin American Citizens (LULAC). The organization is the nation's largest Hispanic civil rights and social service organization.

"If an election were held today, Kennedy would receive 85 percent to 90 percent of the Hispanic vote," Bonilla said.

"The reasons are many. The Kennedy family has long been identified with the underdogs, the poor.The family is Catholic. Hispanic Americans are overwhelmingly Catholic and poor," Bonilla said.

Bonilla and several hundred other Hispanic leaders and community workers came to Washington yesterday to attend the second annual Congressional Hispanic Caucus dinner and to participate in other events marking Hispanic Heritage Week.

President Carter, in a gesture to the Hispanic community, appeared at the dinner and announced two new Hispanic appointments: Abelardo Lopez Valdez to be chief of protocol and Edward Hidalgo to be secretary of the Navy. Carter also reminded the Hispanic audience of his recent action freeing the Puerto Rican nationalists imprisoned 25 years ago for their attacks on President Truman and five members of Congress.

Sen. Kennedy made an eight-minute appearance at a reception before the dinner, but because he was engulfed by reporters and cameramen had almost no opportunity to mingle with the crowd.

At press conferences, parties and private political strategy sessions that included Hispanic members of the Carter administration the talk was dominated by speculation about Kennedy's expected presidential bid and Carter's political survival.

The consensus was stated by the leader of another Hispanic group who requested anonymity "because I have to protect my organization's tax-exempt status."

"Everyone I've talked to on the grass-roots level and in the leadership has told me that if Kennedy goes in, that's it," he said. "Even the Hispanics who support [California Gov.] Jerry Brown are saying that they would leave him for Kennedy if Kennedy declares. That's the reading I'm getting all over."

In the strategy sessions, some Hispanic appointees in the Carter administration were notably ambivalent.

Yes, they conceded, Kennedy probably would win most of the Hispanic vote in a race with Carter. Yes, they acknowledged, a successful Kennedy bid -- which most said they would not oppose -- would place their current jobs in jeopardy.

The problem is that things should not have to be that way, the appointees said in their private meetings.

"It makes me so angry," said one appointee. "All the administration had to do was use some political common sense, to make a few extra appointments here and there.

"Even with the good things they've done for Hispanics, they've screwed up by not selling their record," he said.

Other "political mistakes" made by the administration include the following, according to the appointees who spoke in the private sessions:

The administration has ignored opportunities "to win points" with Hispanic groups.

For example, they said that when rumors began floating several months ago that U.S. Immigration and Naturalization Commissioner Leonel Castillo was in danger of losing his job, the administration did nothing to show support for its top-ranking Hispanic appointee.

Kennedy called Castillo several times expressing support, they said. Castillo, however, later announced his resignation.

The administration also "goofed up on little things like returning phone calls to Hispanic leaders -- really insensitive, stupid stuff," one appointee said.

In discussing Kennedy's vote-getting potential, LULAC'S Bonilla said Hispanic leaders probably couldn't control rank-and-file response to the sentator's "overwhelming charismatic appeal. You go into a lot of these people's houses and you'll find pictures of Jesus Christ in the middle of pictures of Teddy Kennedy's two brothers," [the late President Kennedy and the late Sen. Robert Kennedy.]

"But Hispanic leaders should not be guilty of handing their votes to Kennedy without getting the details of what he will do for our prople . . . That's the mistake we made with Carter," he said.