President Carter did not really mend long-neglected Texas fences, thanks to shortcomings in both style and substance when he addressed some 1,200 black-tie, $500-a-plate diners in the grand ballroom of the Hyatt Regency Hotel.

"I can't believe it," wailed a southwestern politician-businessman who had spent $5,000 in after-tax dollars for a whole table. His disbelief: In the absence of a head table, the president was nowhere to be seen and was actually back in his hotel suite eating a solitary dinner. "Don't worry," a Washington-based lobbyist replied. "He'll be walking through shaking hands while we eat."

The lobbyist was wrong. While Texas arrangers of the dinner requested a walk-through, the White House vetoed it. Nor did the president show up at the mass cocktail party in the hotel lobby preceding dinner. Most diners saw him only when he marched to the microphone bathed in a spotlight, delivered his speech and marched out again.

Having passed up chances to mend those fences through increased personal contact, the president had to rely on one of his shortest suits: oratory. His style was snappier than usual and suitably conservative for this audience but unfortunately built to an anticlimax on energy. While the audience was led to believe he would give them something new, Carter ended with an exhortation for his old energy program (opposed by most of his listeners). Some liked the patriotic appeal, but others shrugged their shoulders at a thrice-told tale.

The fund-raising dinner typified the president's two-day swing through Texas: He did fairly well, but not well enough. "I think he made a dent in his problem," one Democratic insider told us, "but man, he's got a long way to go." The consensus remains that Carter would not carry this vital state today against Gerald Ford or Ronald Reagan.

The problem is not personal animosity but conflict on such key issues as oil and beef, aggravated by 1 1/2 years of neglected politics. The turnout for the Houston fundraiser, grossing over $600,000 for the Democratic National Committee, resulted not only from appeals by two popular Texans - National Chairman John White and Ambassador Robert S. Strauss - but also respect for the Democratic president.

Moreover, Texas Democrats are anxious for Carter to succeed so he will be less of a drag on this year's state ticket. One $500 diner made a bad-news, good-news formulation: "The bad news is that Carter came at all; the good news is that he came in June istead of September." Fear of the Carter drag was expressed by the absence of Rep. Robert Krueger (candidate for the U.S. Senate) and Attorney General John Hill (candidate for governor) at the president's Fort Worth and Houston airport arrivals.

Krueger, making a strong race against three-term Republican Sen. John Tower, campaigns as an "independent Democrat" to stress his un-Carterite posture. As the president arrived in Texas, Krueger attacked the Carter energy policy before an elite Houston businessmen's group. Nevertheless, Krueger that night was struck by the magnetism of the presidency itself and was having second thoughts about campaign appearances with Carter.

But when Krueger went to Austin the next morning to address the Independent Cattlemen's Association, he closely followed Tower's attack on Carter's boost in beef imports. "For God's sake, Bob," a friendly cattlemen advised him, "don't get yourself tied up with Carter." Heeding that advice, Krueger uttered not one encouraging word about his president during a well-received assault on imported beef.

It is too late for Carter to reverse himself on beef or energy. But his tone in Texas was markedly conservative - praising free enterprise, excoriating inflation, traveling the hard road against Moscow.

How much this rhetoric helps is debatable. Although the president's cry that"we are not going to let the Soviet Union push us around" drew cheers from a Fort Worth luncheon, Democratic politicians doubt it narrows the Carter confidence gap in Texas. While conservatives were not convinced, liberals sat on their hands at obvious applause points.

The problem is deeper than issues or ideology, as one prominent, plain-talking Texas liberal (a $5,000 table buyer at Houston) told us after the speech: "Jimmy Carter has lied to everybody in Texas from the blacks and the Mexicans to the oil boys. He has to start over from scratch."

His trip was a modest start, say most Democratic politicians. But he failed to make the most of it; his limp performance in Houston was followed by a widely publicized Army firepower demonstration at Fort Hood costing some $2 million. When the White House permitted the president's anti-inflation theme to the blunted by an Army public-relations spectable, Texas' confidence in the competence of the president and his men was no enhanced.