Even though his esteem in Texas has dropped lower than any earlier Democratic president, Jimmy Carter may yet win this state's 26 electoral votes -- and save his second term -- with a flood of Mexican American and black voters Nov. 4.

Identification, registration and turnout of minority voters have become the beginning, middle and end of Carter's strategy in Texas. It is too late to repair the president's policies that antagonize Texans. Partly thanks to the evangelical political movement, Carter's rural base is eroded. The state's "Anglos" run 65 percent or more for Ronald Reagan.

In Texas-sized proportions, this is the problem faced by President Carter throughout his southern base. Thus, slurs about Reagan's "racism" are not just the politics of excess but a deadly serious effort to energize minority voters. What antagozies editorial writers and cartoonists may impel blacks and Hispanics to vote.

The need is imperative in Texas. Only three Democratic nominees -- Al Smith, Adlai Stevenson and George McGovern -- have lost Texas. No Democrat has been elected without carrying Texas. But Carter's presidential record would have doomed him in the old Texas, where "Anglos" ruled.

"I have never seen a president so poorly regarded," confided one veteran Democratic politician here. "Nobody has a good word for him." Yet, this old pro predicts Carter, now trailing in all polls, will carry Texas. One of his reasons is Reagan's anemic campaign. A better reason is the black-brown vote.

The politically critical arthmetic of minority voting depends on vague approximations. In 1976 when Carter won Texas with 53 percent, the black-brown vote may have been 550,000 (out of 4 million). Carter won an estimated 87 percent of the browns and at least 93 percent (Republicans say 98 percent) of the blacks.

for Carter to carry Texas this year, he must dramatically expand the 1976 minority-voter volume and not fall too far below his share of it then. That is the job of Bob Beckel, a skilled political technician from Brooklyn who left the White House staff (where he had been selling SALT II to Congress) early this year and came here to sell Carter to Texas.

Beckel's registration efforts were expected to yield 800,000 Mexican American voters (compared with 460,000 in 1976) by the Oct. 4 deadline. New black registration is less robust and less measurable. If Beckel can actually get the new voters to the polls, Texas may well be Carter's.

That is why Beckel had no time for much more than lip service responding to complaint's from traditional Texas Democratic politicians that the president's record flagrantly offends Texans: Carter's energy policy seemingly favors the Northest; his oil windfall profits tax enrages small royalty owners even more than corporate titans; the Carter administration is demanding new school busing in Houston.

Lt. Gov. William Hobby and state Attorney General Mark White, two moderately conservative Democrats supporting Carter, have warned the president that his railroad deregulation bill is ruining him politically among lower-to-middle income non-minority Texans. Boosting freight rates for Wyoming coal, they warn, will drive sky-high utility bills still higher and alienate faithful Democrats.

It is among disaffected Democrats that Republican Gov. Bill Clements, calling Carter a "phoney" and "liar," spreads the Reagan gospel. accompanied by former governor John B. Connally, Clements spent the past month setting up Reagan organizations in formerly "brass-collar" Democratic country (so-called because the Democratic Party had a brass collar around voters' necks). Clements' auxillaires there are fundamentalist Baptist ministers including Carter supporters of 1979 who preach for Reagan this time.

Hill County in central Texas is one such Bible-belt, brass-collar area that gave Carter 66 percent of its 1976 vote. Carter strategists acknowledge that is impossible this time. If the county's vote falls below 61 percent, they fear a statewide drop in the rural vote that will require a heroic minority turnout to save Carter.

That is why Sen. Edward Kennedy will visit the Rio Grande Valley late this month to ask his Mexican American following to succor Carter. "I wish Teddy Kennedy would come live in Texas all year," Clements told us, meaning his presence will lose more Texas votes than it wins. Considering Carter's total reliance on minority politics, he has no choice but to take the risk.