The latest published poll gives President Carter a 3-to-1 lead over Sen. Edward M. Kennedy for Saturday's Texas Democratic primary, but that is no safe clue to the outcome.

The betting is that Carter will beat Kennedy 3 to 2 or 2 to 1 for the 152 delegates -- but take that prediction with a Texas-sized grain of salt, too.

This is a system where you have to vote twice on Saturday to make it count, where the weight of a presidential ballot is indexed to the weakness of the last Democratic candidate for governor, and where the results will not be finally known for seven weeks.

"Texas has the worst aspects of a primary system combined with the worst aspects of a caucus system," said Bill Carrick, Kennedy's state coordinator.

"Frankly," said Richard Trabulsi Jr., a key Carter supporter, "there's very little interest in participating, and I don't blame people for being turned off."

Were it not that so many delegates are at stake, both the Carter and the Kennedy camps would just as soon forget about the Texas contest. They have given it short shrift, allocating barely $150,000 between them to the battle for the sixth largest delegation. Kennedy spent only two days campaigning here, and Rosalynn Carter, her husband's Texas surrogate, did no more.

The main thing for campaign-watchers to understand is that the Texas primary results in Sunday's paper will have next to nothing to do with the division of the 152 delegates.

The nonbinding preference poll that will capture the headlines was a last-minute concoction of the state Democratic Executive Committee, seeking to add some glamour to a lackluster primary ballot offering nothing more exciting that a couple of contests for railroad commissioner. It was pushed through to the intense displeasure of the Carter and Kennedy camps -- neither of which wanted to budget money for a Texas media campaign.

The real delegate selection starts with precinct "conventions" held after the polls close Saturday night. Because Texas has no party registration, the ticket of admission to the Democratic caucus is the notation by the voter's name that he or she took a Democratic ballot that day. Thus the plea to "vote twice" on Saturday.

But no one expects more than 10 percent of the primary voters -- mainly the activists -- to come back for the caucuses. "Texans are not used to coming back to vote twice," says Scott Pool, Carter's Harris County (Houston) coordinator. "That's why I'm afraid this could be another Vermont, where we win the beauty contest and lose the caucuses."

The conventional wisdom is that Carter is far ahead in most of Protestant, Anglo, rural and small-town east and west Texas, in the Panhandle and in the Dallas-Fort Worth area. Kennedy has overwhelming support among Mexican Americans and in south Texas and is favored in San Antonio. Harris County -- a cross-section of rich and redneck whites mixed with large numbers of blacks and Chicanos -- is the main battleground in the state.

Pool, a phone company executive, explained the sub-surface reasons why he is "very nervous" about the outcome. The delegate apportionment is weighted toward the minority areas, where Kennedy is strongest, because it is tied to the size of the vote for John Hill, the losing Democratic candidate for governor two years ago. While blacks and Chicanos dominate only one-quarter of the Harris County precincts, they will elect about 40 percent of the delegates because so many conservative white Democrats crossed over to elect Republican Bill Clements governor in 1978.

A similar crossover of conservative Democrats could compound Carter's problems in this primary. A check of Carter leaders in north and west side conservative areas last week found several defections to George Bush, and Pool says, "There's a lot more hustle to the Bush-Reagan thing than on our side."

"Our operation is just not as tight as it should be," the Carter leader said. "The real problem is apathy. There's just a flat lack of interest on our side. You don't find many true believers in the president. There's a feeling he's done as good a job as anybody could, but there's also frustration with him. . . ."

The Kennedy campaign organization was put together very late and it too has a lot of holes. Until his own appearance here Tuesday brought a fresh flow of volunteers, fewer than one-third of the precincts had a Kennedy worker.

But Kennedy has most of the liberal activists who turn out for the precinct caucuses every two years to battle their conservative rivals. His headquarters is in the office building that also houses the following: the Harris County Democrats (the local liberal faction); the consulting firm of Billie Carr, a long-time liberal organizer and Democratic national committeewoman; ACORN, a community-organizing group; the Houston Urban Bunch and Harris County Tenants Alliance, both neighborhood groups; the Gay Political Caucus; the Feminist Credit Union and Women's Center; and CAN-IT, an anti-nuclear group.

A bemused Joanne McGuire, Kennedy's only outside paid staff worker, said, "One night I spoke at three meetings for Kennedy and I didn't even leave the building."

Labor is split, with the teachers, communications workers, construction and maritime trades for Carter, the steelworkers, machinists, and state AFL-CIO for Kennedy.

Key community leaders are hedging their bets. Rep. Mickey Leland, a fire-brand black leader, surprised people by getting off Vice President Mondale's campaign plane and endorsing Carter. But his mother and brother were conspicuous at Kennedy's side during the senator's Houston visit.

Similarly, Ben Reyes, a city councilman and influential Mexican-American leader, introduced Kennedy at City Hall, but -- to the discomfiture of the Kennedy camp -- his brother Tony, the best organizer in the family, attended the reception the next morning for Rosalynn Carter.

Adding to the uncertainty is the fact that the voting for national convention delegates will not actually take place until the June 20-21 state convention. Preliminary estimates of Kennedy and Carter strength will be made after Saturday's precinct caucuses and May 10 county and senatorial district conventions. But no pledges are binding until June 21 -- long after the last set of primaries in other states.

Carter has some powerful Texas arm-twisters: his national campaign chairman, Robert S. Strauss, Democratic national chairman John C. White and White House assistant Sarah Weddington. The pro-Carter state chairman, Billy Goldberg, said that by June 21 "the contest will probably be decided and I would hope we have a unanimous delegation."

No one else seems to think that is likely, but few other people share Goldberg's enthusiasm for the Texas system, either. "There's a lot to be said," he said, "for the smoke-filled room."