Today's Republican runoff in the west Texas 19th Congressional District cannot come a moment too soon, as far as relations between Ronald Reagan and George H.W. Bush are conerned.

The former California governor and the former Republican national chairman - both unannounced aspirants for the GOP's 1980 presidential nomination - have been drawn into the fight between Bush's son, George W. Bush, and an ardent Reagan backer, Jim Reese.

"I'm not interested in getting into an argument with Reagan." Bush, the former Central Intelligence Agency director and head of the U.S. liaison office in Peking, said in an interview. "But I am surprised about what he is doing here, in my state . . . They are making a real effort to defeat George."

Reagan, through his spokesman, Mike Deaver, said he had assured the elder Bush in a phone call last week that he had no animus toward young Bush's candidacy. But he did not back away from his support of Reese.

The two men are seeking the Republican nomination for the seat being vacated by Rep. George Mahon (D-Tex.), the chairman of the House Appropriations Committee. Despite Mahon's 44-year tenure, Republicans have hopes of winning in the conservative oil and agriculture district reaching up into the Texas panhandle.

Reese, the former mayor of Odessa, received over 45 percent of the vote against Mahon in 1976. But he trailed Bush, an oilman, by 808 votes in the May 4 primary. A third candidate, who received 11 percent of the vote, denied either man a majority and forced today's runoff.

According to Deaver, Reagan had endorsed Reese in his 1976 campaign against Mahon, and backed him again in this year's primary when the third candidate, Joe Hickox, implied that Reagan's silence meant that the endorsement of Reese had been withdrawn.

Citizens for the Republic, a political action group run by Reagan's political lieutenant, Lyn Nofziger, gave Reese a $1,000 contribution four days before the primary and added another $2,000 six days after he began his runoff campaign against Bush.

According to Deaver, Reagan "was not aware" of either contribution, because he was out of the country when they were made.

Reagan's spokesman added that a week ago, the former governor called the elder Bush to say he would have no further involvement in the race and would gladly campaign for young Bush if he were nominated.

But relations soured further last Monday when Clarence Warner, the Oklahoma Republican national committeeman and a key leader in Reagan's 1976 presidential campaign, came into the Midland-Odessa airport and called a press conference to endorse Reese.

Warner and a colleague, J.C. Lewis, raised the issue of the elder Bush's membership on the Trilateral Commission, a group of leading European, Japanese and American business and political figures organized by David Rockefeller. The Trilateral Commission - to Which President Carter and many leading officials of his administration formerly belonged - has been a target of criticism from both left-wing and right-wing organizations.

The charge apparently was aimed at buttressing Reese's contention that young Bush, who was born in Connecticut, was a liberal Republican with close ties to the Rockefeller family.

Young Bush called a press conference Thursday to ridicule the charge and condemn what he called attacks on his father's loyalty and integrity.

The elder Bush and Reagan are regarded as potential rivals in the 1980 Texas primary. In 1976, Reagan won an important victory over President Ford in Texas. Bush would probably have to win his home state to give credibility to his expected candidacy in 1980.