Bedeviled by an opponent who favors jogging garb, 75-year-old Sen. Warren G. Magnuson (D-Wash.) concedes that his shuffling gait doesn't get him around very fast anymore. But he says it doesn't matter. "The meetings don't start till I get there," boasts the gruff, stubborn and very powerful chairman of the Senate Appropriations Committee.

Several states away, as his opponent campaigns on the no-so-subtle theme of "Energy of the 80s," Sen. Barry Goldwater (R-Ariz.), age 71 and hobbled by a hip ailment, buys television time to make the point that running foot races doesn't win influence in Congress.

Just as age and related encumbrances helped deny Sen. Jacob K. Javits (R-N.Y.) the Republican nomination for reelection, they are giving Magnuson and Goldwater -- once almost untouchable fixtures of Western politics -- their toughest reelection campaigns in years, perhaps ever.

Both are favored in polls, but so was Javits. The age issue is a tricky one for both sides and difficult to gauge. "When the Javits thing happened, a shock wave ran through the campaign," said Aubrey Davis, Magnuson's campaign manager. "It's basically the only issue in the campaign."

What is protecting the two Senate veterans is the prestige and power that their relatively small states derive from their senior senators -- from Goldwater's ability to inspire conservatives and from Magnuson's no less impressive ability to enrich Washington state.

While Magnuson stresses the many bridges, dams and jobs he has brought home, Goldwater's main campaign brochure passes lightly over his own pre-Senate work in launching the Central Arizona project for water development and stresses his role "for more than 20 years . . . . as the voice of America's conscience."

Bill Schulz, his Democratic challenger, acknowledges Goldwater's stature as a state and national landmark and praises his conservative policies, which come close to holy writ in conservative Arizona. But Schultz contends Goldwater has lost interest in the job and should be given a well-deserved rest. "He's a great American who's no longer giving full attention to his job . . . . He was hot-boxed by his Republican friends into running again against his wishes," argues Schulz.

The closest Schulz has gotten to a frontal attack on Goldwater has been to assail his record of absenteeism over the last six years, which he says is "absolutely the worst in the Senate," worse even than that of the late Jim Allen (D-Ala.), who died two years ago. Goldwater snaps back that "that little bit of jazz" simply shows Schulz's ignorance of the Senate, where, he maintains, the major business is done off the floor.

As for his age, Goldwater grins and growls, "I don't buy the argument that age is the determinant of senility. I know some 30-year-olds who are senile as hell."

But the lost-touch argument has taken some toll. "I know people who go back to Washington and say they can see anyone but Goldwater," complained Len Hanzlick, a southern Arizona rancher. "Honestly, they think he's a phantom."

Schulz, a 49-year-old multimillionaire apartment developer from Phoenix and graduate of West Point and the Harvard Business School, shares Goldwater's fiscal posture, although he draws the line on matters like Medicaid-funded abortions, which he supports along with the Equal Rights Amendment. "My politics could easily pass for Republican in many states," says Schulz, "but the difference is that I have a passionate commitment to make the system work for the have-nots."

The amiable, balding Schulz is an attractive, vigorous campaigner, and is pumping $1.3 million of his $10 million fortune into the campaign, forcing Goldwater to raise a planned $700,000, vastly more than he's ever had to spend before.

Arizona is growing fast, which could be an advantage to a fresh-faced challenger. But Schulz's polls tell him he does better with old Arizonans than with the 800,000 newcomers who arrived since Goldwater last ran six years ago, many of them relatively affluent retirees who voted for Goldwater for president from other states in 1964.

Goldwater could be hurt by an impression, nurtured by the opposition, that he was a reluctant candidate prodded into running for a fifth term by Republican colleagues in both Washington and Arizona who figured a weaker GOP candidate might lose the state. He insists he never thought of retiring and has rebounded well from hospitalization for hip problems last summer. But longtime Goldwater backers have been heard to say they will do him a favor by voting for his retirement next month.

The most recent Arizona Republic newspaper poll, taken earlier this month, showed Goldwater leading by 10 percentage points, down from 15 points a few weeks earlier. Schulz's poll shows the challenger trailing by only a few points.

If Goldwater's appeal is to the old-time religion of political conservatism, Magnuson's is to the time-tested lure of political pork.

"The relief efforts for Mount St. Helens, the West Seattle and Hood Canal bridges, funds for youth job programs, medical health research and neighborhood health clinics, contracts for the Todd shipyards, jobs in our port cities, aviation and fishing industries," asserts a television ad -- not from an entire career but just during 1980 -- "the 36th year of that kind of accomplishment for this man, Warren Magnuson."

The campaign year booty ranges from a staggering $951 million for Mount St. Helens disaster relief to $1 million for a Seattle waterfront trolley line, with plenty more sandwiched in between.

The man who is running against Santa Claus is Slade Gorton, 52, the state's popular, trim and athletic three-term attorney general, a moderate Republican of the kind that often gets elected in Washington state.

Like Democrat Schulz in Arizona, Republican Gorton doesn't even try to deny his opponent's accomplishments.

Instead, using a left-pocket, right-pocket analogy, he contends that Magnuson is only giving back what he's taken from taxpayers by espousing national economic policies that have produced inflation, unemployment and high taxes and interest rates. "If people want 14 percent inflation and 8 percent unemployment . . . they should reelect Magnuson because he's more responsible than any other member of the Senate for this situation," says Gorton.

To the dismay of Sen. Henry M. Jackson (d-Wash.), Gorton has tried to use the popular Jackson as a reason for retiring Magnuson and building a new line of seniority. The 68-year-old Jackson will probably retire in a term or two, leaving the state without seniority if Magnuson hangs on until then, too, Gorton argues. "If seniority is so important," his campaign literature proclaims, "let's never lose it."

Gorton's television ads are even more graphic. A young farmer sits next to his aged father and says, "Poppa says when Warren Magnuson went to Washington Roosevelt was president . . . you know, out here on the farm, we rotate our crops. Don't you think it's time we rotated our Senate crop while 'Scoop' Jackson is still one of the most senior senators?" An angry Jackson cried foul and said the Federal Communications Commission should look into the ads.

Magnuson, however, has trotted out his own young farmer on television to say, "Sure he's old . . . . So what? . . . Maggie's doing the job."

Even more than Goldwater, the portly "Maggie," as he's universally known here, looks his age. His hearing is impaired and his gait is slowed by an old knee injury and arthritis. His campaign schedule is carefully paced to give him ample rest time, favoring events like a highly successful whistle-stop train trip last summer. Newspaper stories on his health speak of his heavy drinking in the past, but say it has tapered off. His doctors say he's as healthy as might be expected for age 75, and his radio ads say he's "still raring to go."

Magnuson, favored by corporate political action committees, labor unions and the Seattle financial establishments, will outspend his rival, who sued a lot of big-money interests in the state as attorney general, by more than 2 to 1 by election day.

Magnuson is counting on $1 million or more, Gorton on $500,000 or less.

Mother Nature may also be on Magnuson's side. Every time Mount St. Helens goes off -- and it just went off again -- it is a reminder of the Magnuson largesse, even though Gorton makes a point that the federal bureaucracy that Magnuson has fostered has delayed receipt of the relief money in Washington state. "We sometimes think Magnuson has a button to push to get that mountain to respond on cue," sighed Gorton aide Kirk Smith the other day."