On a bright, sunny day in Sacramento last week, Gov. Edmund G. (Jerry) Brown Jr. smiled at reporters and said he would take "the high road" in the dwindling days of his reelection campaign. Then he accused opponent Evelle J. Younger of lying and compared him, alternately, to Huey Long and Karl Marx.

On the same day, state Attorney General Younger flew the 775-mile trip from Los Angeles to Sacramento and back in an effort to obtain the endorsement of Paul Gann, coauthor of Proposition 13. He didn't get it, even though he signed a new Gann initiative petition for a state spending limitation.

These two incidents, takes together, could symbolically represent much of the campaign between Democrat Brown, who is aiming for a million-vote victory, and Republican Younger, who is having a difficult time convincing his financial backers that he has any chance at all.

With just a week to go before the election, even Republican Party officials admit that Younger has fallen to far behind Brown that he had only a remote chance of overtaking him.

At campaign stops throughout the state, Brown is taunting Younger as "a big spender" interested only is his pensions and perquisites. Younger, with a lighter schedule, is drawing small crowds and appears mostly to be going through the requisite political motions.

The race did not always seem so onesided. Younger, relying on name recognition acquired during his eight years as attorney general, ran an effective primary campaign against three opponents. He won easily and entered the campaign against Brown with a united Republican Party behind him.

Meanwhile, Brown was sinking in the public favor he had cultivated and enjoyed during the four years of governorship. The reason was Proposition 13, which Brown, during the primary campaign, called "consumer fraud, a rip-off, a legal morass and a long-term tax increase."

California ignored all such denunciations of the property-tax-limitation initiative and passed it by nearly 2 to 1. Furthermore, many voters were angry with Brown for criticizing the tax-cut initiative. A survey taken by pollster Mervin Field a week before the primary showed the governor slipping so badly that he led Younger by only a single percentage point.

After the June 6 primary, however, Brown lived up to his reputation as one of the nation's most adept politicians by claiming political title to the initiative he had opposed. Speaking of himself as a " born-again tax cutter," he pledged to make Proposition 13 work and then sponsored a $1 billion state income tax decrease.

The governor won over even Howard Jarvis, the other coauthor of Proposition 13, who, after making a television commercial for Younger, decided to do an even stronger one for Brown. In this TV spot, Jarvis says he "knew Gov. Brown was the man who could make it [Proposition 13] work."

Joking about his transformation, Brown told a fund-raising gathering at Hugh Hefner's mansion: "I don't believe in pride of authorship.When I see a good idea, I'm prepared to steal it."

While Brown was gaining credit for the work of Jarvis. Younger vacationed in Hawaii, then underwent a kidney-stone operation.Younger had supported Proposition 13, but polls showed that many voters thought he had opposed it while Brown has backed it.

"Proposition 13 was an incredible political event that captured the public's imagination," says pollster Field. "When all the cameras were focused on Sacramenta and the political process. Younger decided to move offstage."

Brown did not depend on Proposition 13 alone. Campaigns in California traditionally start on Labor Day, a series of hard-hitting radio and TV, but Brown opened up in July with commericals that directly attacked the competence and integrity of his opponent.

The commericals were classics of negative advertising, even in a state with a tradition of vituperative and highly personal politics. Among other things, they alleged that Younger had make "government office improvements at taxpayers' expenses" and make gifts to friends from public funds.

The office improvements turned out to be showers in two Younger offices - one of which apparently was installed by Brown's father, former governor Edmund G. (Pat) Brown. The gifts were books and Justice Department glassware that Younger paid for himself. But the ads set the tone for Brown's most effective attack, which is that Younger lives off the public trough with multiple pensions while calling for reduction in government spending.

Younger currently draws more than $1,400 a month in pensions earned as an Air Force officer, a Los Angles judge and district attorney. When he starts drawing the pension he has earned as attorney general, Younger will be receiving $53,226 a year from four government pensions.

The ads angered Younger's wife, Mildred, who replied that members of Brown's family draw $250,000 a year in pensions and other public funds. But the Brown commericals put Younger on the defensive, and Brown has kept him there.

The central issue of the campaign, says Brown, is "the integrity of Evelle Younger," whom hecalls "Brand X" and "a certified deceiver . . . who does not tell the truth."

Younger has not been above unsupported charges of his own. He has said repeatedly and without evidence that Brown favors "forced busing" because he signed a bipartisan bill to help the Los Angeles school district pay some of the costs of a court-ordered desegregaton plan.

And in their first of five face-to-face televised encounters, the normally mild-mannered Younger startled viewers by casually calling Brown "the worst governor in the modern history of California."

But Younger's efforts to label Brown as a big-spending liberal have failed. The state is enjoying unprecedented prostperity, which Brown cites as the major reason for his big lead, and the governor is widely viewed as a better budget-cutter than Younger.

Brown's fiercest critics now are from the left side of the California spectrum, such as the Americans for Democratic Action, which charge that Brown's "commitment to progressive government has weakend as his presidential ambitions have grown."

Brown, who defeated Jimmy Carter in five presidential primaries in 1976, turns aside all questions about future presidential quests by saying he has "lowered his expectations" since Carter's achievements at Camp David toward a Middle East peace. Even so, he rarely praises Carter on any other issue. When asked whether the "lowered expectations" line meant he was ruling out running for president, Brown quickly answered "No."

And in contrast with the 40-year-old Brown, the 60-year-old Younger's interest in politics is less than all-consuming.

While Brown spends seven days a week campaigning, Younger takes time out to socialize, go to football games and be with his family.

The polls indicate that Younger will lose - and badly. Late in September, Field's California Poll showed him 14 points down. The Los Angeles Times poll on Monday found Brown leading him 54 to 34 percent, with 4 percent for other candidates and 8 percent undecided.

As Field sees it, the judgment of the election is likely to be that Younger "failed to make capital out of the public's fairly widespread negative view of Jerry Brown."

"Perhaps half the California voting public was ready to vote against Brown," says Field. "They considered him opportunistic on Proposition 13. What occurred after the June primary was that a lot of voters started looking at the alternative. The alternative was Evelle Younger."