The Young, the Old and the Restless, a multimillion-dollar political soap opera, has been staged this sesquicentennial year by Texas Republicans eager to prove that they can display as much talent and spirit -- and attract as much money and publicity -- as the state's Democrats, who were the only actors for most of the first 150 years.

In featured roles are Young Tom Loeffler, the suburban cowboy congressman from the Hill Country who wants to ride his horse Liberty to the governor's mansion, carrying the theories of the Reagan Revolution in his saddlebag; Old William Clements, the crusty Dallas oilman who was the state's only 20th-century Republican governor and who badly wants to avenge his 1982 defeat by Mark White; and Restless Kent Hance, the country lawyer from Lubbock who two years ago was a conservative Democrat in the Senate primary, then switched parties in search of better opportunity, which quickly availed itself in the form of a campaign for governor.

An interesting cast of characters. But the show's first run closes Saturday, primary election day in Texas, and it never really caught on. The internal politics of a resurgent Republican Party have been overshadowed by a far more powerful melodrama: The Great Oil Slump of 1986. "The people don't seem to care one iota about politics right now," said Loeffler, articulating the prevailing sentiment. "They're too concerned about the economy."

Especially in Houston, considered the key to winning the primary because about a third of Republican primary votes are cast there, political rhetoric seems secondary if not irrelevant. There is little connection between the race and the energy recession that has devastated the local economy. All three candidates took the most popular Texas position on the issue, supporting an oil import fee, but they would not criticize two fellow Republicans who have opposed it: President Reagan and Texas Sen. Phil Gramm.

"You are not going to get the president to change his mind by criticizing him and lambasting him," Hance said.

Most of the lambasting in the Republican primary has been directed elsewhere, at Gov. White, the Democrat who is seeking a second four-year term. The Republicans for the most part have adhered to party chairman George Strake's "11th Commandmant" directing them not to attack one another. There have been no major issue disputes, no serious gaffes by Clements, the front-runner, and no concern that the losers will not unite behind the victor.

"We have a good understanding of one another," Clements said. "We can probably trade speeches and each make the other's if we had to."

As much as possible, they have tried to blame White, rather than Reagan or Saudi Arabia, for the state's energy-related fiscal crisis, saying that his refusal to call a special session of the legislature resulted in Standard & Poor's decision to lower its bond rating from AAA to AA+ on several Texas government agency debts.

With the economy in such poor shape -- the state deficit is at least $1.3 billion -- and several interest groups, such as teachers and the parents of children in private Christian schools, upset at the White administration's policies, the governor has been forced to campaign hard even though his own primary opponents are relatively unknown and very much underfinanced. One of those opponents, A. Don Crowder, claims that a poll this week showed White would not win the 50 percent necessary to avoid a runoff. Several Democratic officials said such an outcome is unlikely but possible.

There is a widespread feeling that the polls might be less reliable than usual this year, partly because voters apparently have not yet focused on the campaigns. One survey indicated that there might be as many or more ballots cast in the Republican primary as the Democratic one, a stunning development because even though more Texans are beginning to identify themselves as Republicans, Democrats usually turn out at least two times as many voters in primary elections.

To headline writers the campaigning this year, which once promised duels and shootouts, has been a "snoozer" and a "snore." To political analysts, who hoped to find lessons in how and why the Republican Party has surged in the South and Southwest, the happenings have not necessarily jibed with their preconceptions and suppositions.

Clements, who entered the race last, appears to be holding a comfortable lead. Most polls show him with slightly more than the 50 percent he needs to avoid a runoff against the second-place finisher. And the latest poll, released by the Houston Chronicle yesterday, shows him solidifying his lead.

The resurgence of Clements has been the biggest political suprise of the year in Texas. During his tenure as governor between 1978 and 1982, and especially during his last campaign against White, Clements disillusioned many Republican Party workers, who thought he was arrogant, grumpy and more concerned with his career than with the party. After Clements left office, Gramm switched parties, got elected to the Senate and emerged as not only the leading GOP figure in the state but also as the symbol of the new shape of the Republican Party: younger, more ideological, more aggressive in converting conservative Democrats to the Republican Party.

Hance is Gramm's prime convert. He switched parties last May and soon announced for governor, bolstered by the money of Dallas banker Bum Bright, owner of the Dallas Cowboys, who had been a longtime Clements supporter. One of Bright's lieutenants, Jim Francis, who had managed Clements' campaigns, came along to help Hance. But after luring Hance into the race and helping him hook up with Bright and Francis, Gramm backed away, refusing to endorse Hance over Clements and Loeffler.

"Gramm got Hance out there and just sort of let him hang," said one Republican consultant. "The stronger Clements looked, the less you heard about the Gramm-Hance relationship."

Hance has based much of his campaign on trying to persuade conservative Democrats to vote in the Republican primary. If the polls that indicate a heavy turnout prove correct, he will have a better chance of finishing second and forcing Clements into a runoff. Hance is confident he could beat Clements or White head-to-head, but he's not as certain about this three-way race. "I'd be hell in a general election," said Hance, who in 1984 lost in the Democratic primary Senate runoff, "if I ever get to one."

Many Republicans feel that White's most vulnerable area is what they see as a lack of credibility. They claim that he has promised far more than he has achieved.

Hance, who has said that in his final years as a Democrat he often publicly endorsed candidates, such as Walter F. Mondale for president and Lloyd Doggett for Senate, that he privately opposed and voted against, may have credibility problems himself.

Loeffler's key problem is that he is perhaps better known in Washington than in Texas. His political career in the House has been upwardly mobile -- at 39 he is the Republican deputy whip, ranking third in the leadership. But very few House members are known outside their districts. And that holds true for Loeffler, whose district includes parts of San Antonio and west Texas out to Midland.

When Loeffler started the campaign, his name recognition was well under 10 percent. And though he has spent heavily in TV advertising, he is less well known than Clements and Hance. Part of the problem, according to one Republican consultant, is his rather plodding nature. "The guy is in desperate need of a charisma bypass," said the consultant. "But if he gets into the runoff against Clements, he might get some charisma in a hurry.