Texas Democrats, normally a fractious and disagreeable bunch when confined to a small area, met harmoniously here this weekend to select a heavily pro-President Carter delegation to the national convention -- and then almost forgot to say anything about their candidate.

As these events go, the state convention was relatively placid, with unity the theme and defensiveness the tone. There was only one reported fistfight and few floor squabbles. About the most outrageous public comment came from a non-Texan, Rep. Rich Nolan of Minnesota, who said the soil erosion problem is as much a threat to the country as is nuclear war.

The convention's outcome was never in doubt, and though a few activists worried about the final delegate count, only the people hoping for a ticket to New York for the August conclave really cared. So whipped were the forces of Sen. Edward M. Kennedy that they joked about having a herd of goats set loose just before the opening session in hopes of postponing the inevitable. A stampede for Kennedy, they were going to call it.

In this summer of Texas chic and urban cowboys, the gathering was marked by more suits than bolts and as many farmers' caps as cowboy hats. Only the ever-present teachers union displayed much regionalism, with Texas-shaped buttons reading, "The Best Little Poorhouse in Texas."

The convention was a symbol of the changing nature of politics here, where the Republicans captured a governorship in 1978 for the first time in a century and the liberals have begun to consolidate their strength in the Democratic Party.

Nowhere were the changes more evident than in the rising influence of the Mexican-American community, and it was that group that drew the most attention from the Carter-Mondale forces as they prepared for a tough fight in November against the expected Republican nominee, Ronald Reagan.

Mexican Americans, who supported Kennedy by better than 2 to 1 in the May 3 primary, were courted vigorously all weekend by the Carter forces. On Friday, the White House used a meeting of Mexican-American Democrats to announce that veteran Texas state Rep. Matt Garcia would be nominated to head the Immigration and Naturalization Service.

On Saturday, despite their allegiance to Kennedy, Mexican Americans emerged with 30 of the 152 national convention delegates, five more than their quota and seven more than the largely pro-Carter black community got.

It was, as former state legislator and gubernatorial candidate Frances (Sissy) Farenthold told the convention, "a striking forecast of the future of Texas."

Although Carter beat Gerald R. Ford here in 1976, he is considered an underdog against Reagan, and the importance of Texas to his reelection effort was demonstrated by the appearance here of Tim Kraft, Carter's campaign manager. It was the first state convention Kraft has attended, he said, and he came to San Antonio to begin building bridges to the Kennedy supporters who are being counted on heavily in the fall campaign.

"We've got to win over South Texas, the valley, San Antonio and other areas where we took a pasting in the Mexican-American community," Kraft said.

In the May 3 primary, 36 percent of registered Mexican-American Democrats voted, a percentage that exceeded that of the overall turnout for the first time. Because of ongoing voter registration efforts, the number of Mexican Americans who voted in the primary -- 270,000 -- almost matched the 278,000 who voted in the 1976 November election, where turnout among Mexican Americans was about 55 percent.

Carter won 87 percent of the Mexican-American vote here in 1976 and needs to do about that well again to beat Reagan. But he has two problems: getting Kennedy supporters to come over to him in the fall and generating enough enthusiasm to get Mexican Americans to go to the polls.

The state party plans to spend $600,000 on a targeted voter registration and get-out-the-vote drive this fall, according to Gary Mauro, the party's executive director. More than $100,000 for that was generated at a fund-raiser in Houston Thursday, another reason for Kraft's journey to the state.

"Democratic turnout," Kraft said, "is absolutely critical."

While some Mexican Americans said this weekend they would not support Carter under any circumstances this fall, their leaders' tone was more conciliatory.

"The bottom line is that we've got to be together to get out the vote to defeat Ronald Reagan," said Ben Reyes, a Kennedy supporter and one of the rising Mexican-American leaders in the state.

But it will take the organizational efforts of the Mexican-American leadership as well as what Kraft calls a "visible and aggressive" campaign by the president to carry it off.

Kraft said the Democrats "can take this administration's record with pride to South Texas and regain the support of the Mexican Americans," but judging from the state convention, Carter may have to do it himself. No one among the Democratic establishment seemed willing to lavish praise on the president, even at a convention overwhelmed by Carter supporters.

Texas Democratic officeholders past, present and future paraded almost endlessly before the 7,800 delegates and alternates, but the name Carter was rarely mentioned. When it was, it was in a defensive plea for unity. "If I can bury my differences with Jimmy Carter, then every Democrat can," said Lt. Gov. Bill Hobby.

Party leaders invoked John Steinbeck, Mark Twain and Winston Churchill ("never quit. NEVER quit. NEVER QUIT."), not to highlight the president's record but to warn of disaster in disunity which they said could lead not only to defeat in November but also to the reelection in 1982 of "our temporary, Republican governor" Bill Clements.

But, if nobody came to praise Carter, few felt passionate enough about anything to condemn him, except for a band of angry farmers from the Panhandle who formed the core of the uncommitted and who hoped to start trouble by supporting a resolution calling for an open convention in New York.

The resolution lost easily on a voice vote denying Carter coordinator Robert Beckel the roll call that would have demonstrated how disciplined the Carter forces were.

And, in the spirit of unity, almost every group got something, an indication of what things are likely to be like in New York in August. The farmers got several resolutions they wanted and party activists had a little fun knocking off a couple of leaders.

Only the Lesbian-Gay Caucus went home without anything, as the convention rejected two gay rights resolutions. But that fight ended humorously when the leader of one district delegation stepped to the microphone to announce results on a motion to table one of the two resolutions.

"Mr. Chairman, I don't exactly know how to put this," he said. "We've got 141 against tabling, we've got 20 for tabling. And we've got two who can go either way."