THE WHITE HOUSE theater is alive with the six-shooters and singing of "Paint Your Wagon" when a messenger tells President Carter that the vice president is calling. And it's important.

Reluctantly, Carter ends his evening of musical cowboys and goes upstairs to a "secure" phone. Walter Mondale gives him a quick fill. He learns that his advisers are locked in what Carter will later call "a heated difference between Fritz on the one hand and Cy and Zbig on the other." The issue is a firmly worded portion of a speech Secretary of State Cyrus Vance will deliver the next day at the United Nations.

What Mondale does not know is that Carter had already decided, basically, that the draft Vance had sent him was fine.

What Carter does not know is that Mondale had seen the Vance draft a day or so ago and had sent the secretary a revision suggesting softer language on the Palestinians and the West Bank -- only to just learn that Vance submitted his original draft to the president anyway.

What Vance does not know is that Mondale is now calling the president, to make a final, direct bid for more moderate language. (What Brzezinski does not know is unknown.)

While Carter is listening on the secure phone upstairs and Lee Marvin is singing in the movie theater downstairs, Mondale makes his case that the United States will only further inflame the situation by trying to pressure Israel into concessions with a hard, public line. Carter listens and he agrees. He hangs up and calls Vance in New York and instructs him to use the more moderate wording in his speech the next day, Sept. 29, which of course, Vance does. The speech draws praise from both the Arabs and the Israelis -- "and it would have been quite different otherwise," Carter says later.

What the American public does not know is that the vice president has quietly won an intra-administration disagreement. And this should be big news because the American system just has not been geared to produce that sort of influence in that job.

NOVEMBER, 1978.

The vice president is frowning, which is a look that is rather out of place on the easygoing Fritz Mondale face. He has stopped puffing on his long, dark made-in-Tampa; he is twirling it now, between thumb and forefinger, like one of those worry stick gadgets of the late '60s.

"That's a problem for me -- a real problem," he says. He has been asked, since the president considers him his "chief staff person," just where he has made a difference. "You see, I really don't know how to answer that. What I mean is, I really hate to get into that sort of thing... I feel my relationship with the president is personal, confidential, and it must be kept that way if it is to be effective."

The interviewer is not above a little light goading. Did Mondale ever win a dispute with Cy Vance? No comment. "Well, you have to start putting out a few of those stories if you expect people to believe that you are your own man," the interviewer says.

"No I don't," the vice president says.

And he does not. Instead, he says, he has asked the president to talk with the journalist about just what sort of vice president Mondale is. The president can reveal whatever he wants about their confidential chats, says Mondale. "Besides," he adds, "my Dad always believed that you should be spanked for bragging about yourself."

The next day, the president telephones the journalist to brag about his vice president. "You doing a story about Fritz?" he asks. Mondale would not be the source of a story about the Vance speech. But Carter would. He volunteers the tale without hesitation. "Fritz, almost alone, felt we were making a mistake," Carter says. "And he was right..." Carter goes on to add other examples as well: Mondale being valuable on the Mideast, the Bakke case, SALT, with Congress. He is clearly anxious to do all he can to emphasize the importance of his vice president. He concludes:

"Fritz Mondale's about the best thing that ever happened to me -- after I got Rosalynn for a wife. I don't know anything that's been more gratifying than to have Fritz as vice president."

THE VICE PRESIDENCY was created by the Constitution to be a sort of appendix on the federal body politic. Vice presidents, like queen mothers, are important people with nothing important to do.

But if the one constitutionally prescribed role of the vice president is to be ready -- ready to assume the presidency at a moment's notice -- then it must be said that Walter Mondale is easily the most ready of any vice president, at least in the modern era.

It is in part due to the system. As Carter and Mondale have set it up, the vice president is a generalist, an all-purpose adviser. He participates in virtually every major decision that the president makes, foreign and domestic; and those he does not participate in, he is informed of. He is aware of the various alternatives that were considered, and the reasoning that went into the final decision.

This may not seem like a break-through of great magnitude, but remember April 1945: Harry Truman assumed the presidency without even knowing of the existence of the atomic bomb that he would just months later, order into use. In the years that followed, Vice Presidents Nixon, Johnson, Humphrey, Agnew, Ford and Rockefeller all found themselves at times scorned, at times demeaned, and often shut out of the decision process -- all courtesy of the president and his staff.

Back in the transition days of December 1976, Carter ended a Blair House meeting with Mondale by promising that this time it would be different. "But the history of vice presidents is grim," Mondale replied. "And I'd be surprised if this works out differently." So far, Carter has seen to it that it has. Carter has scheduled himself to have lunch privately once a week with his vice president (he is also scheduled once a week to have lunch privately with his wife.)

Then there is the collegiality. It was at Carter's urging that Mondale made his office in the west wing of the White House, between those of Hamilton Jordan and Zbigniew Brzezinski, below the congressional liaison quarters of Frank Moore and the domestic affairs office of Stuart Eizenstat, and just around the corner from the Oval Office. And to hear the Carter upper echelon tell it, there must be days, perhaps in the cold quiet of winter, when the first floor west wing of the White House assumes all the salient characteristics of a Hamilton Beach corn popper.

"Firtz will pop into my office a couple of times a day," says Jordan, "or I'll pop into his... you know, to discuss a problem or just to kid."

"Fritz is always popping into my office, or I into his," says Brzezinski...

"Ham or Zbig or Frank or Jody are always popping into the office," says Mondale...

"I'll pop into Fritz' office a couple of times a day," says Frank Moore...

"We're all just kind of popping in and out of each other's offices all the time," says Jody Powell.

All of that is on the inside, where Mondale is now presiding over the drafting of the 1979 Carter legislative agenda, and the like.

On the outside, where the inner spinning is not seen and the collegial popping is not heard, there is little evidence that Fritz Mondale is much different from all the other vice presidents. When there is an announcement or presentation to be made that the president does not have the time or inclination for, Mondale is trotted out to do the honors. For the election season, Mondale was dispatched to the hustings, just as all the Spiro Agnews had been before him. (This fall, Mondale distinguished himself more in total mileage than in results; the Republican sweep of his own Humphrey-Democrat Minnesota could only be viewed as a stunning Mondale defeat, even though in fact he was not as responsible personally as was the entire Democratic Farmer-Labor-Party, which conducted politics '78 like the firing squad which marches into a circle and commences to shoot.)

And there is the cheerleading. In 1975, Nelson Rockefeller decided that the official vice presidential seal did not reflect the true significance of the office and so he gave new macho to the eagle by stuffing 13 arrows in its claw. But he forgot the megaphone and pom-poms. Because vice presidents traditionally fall all over themselves to lead the cheer-leading for the president.

Spiro Agnew did it literally. Remember him, back in the days when nabobs were nattering, falling on the Andrews Air Force Base tarmac, but then climbing to his feet and insisting on delivering -- in full nosebleed -- a moving, fullblown tribute to Richard Nixon, just back from overseas.

Hubert Humphrey did it always.

And, especially in the first year, so did Fritz Mondale. Dutifully and sometimes exuberantly, he resorted to full-oak phrases to describe acorns of accomplishment. 78I think this has been one of the most successful congressional sessions in a long, long time," he bubbled to reporters at the end of a first year that produced only scattered victories at best. "... The session responded to presidential leadership."

BUT THE DIFFERENCE between Mondale and his predecessors does exist. It lies both in the readiness factor and in the relationship that seems genuine between this president and his vice president. Carter does look to Mondale for advice often, "three or four times a day," he says. And he is not reluctant to tell the public about it. A year ago, Carter telephoned two reporters when he heard they had been asking around whether Mondale had lost his influence within; not true, Carter said, and he went on to detail some examples then. Again this year, he was anxious to talk up Mondale to a journalist.

Of course other presidents have been known to talk of the accomplishments of their vice presidents.

Consider the press conference of Aug. 24, 1960:

Question: Mr. President, what major decisions of your administration has the vice president participated in?

President Eisenhower: If you give me a week, I might think of one.

And then there was Lyndon Johnson. Having suffered the humiliation of seeing his vice presidential perks pulled like impacted molars in the Kennedy years, he seemed to take perverse pleasure in the long, slow humiliation of Hubert Humphrey.

The story got a bit of mileage around the cocktail circuit because it was so typically LBJ. And because people knew it summed up exactly how Lyndon Johnson felt about his vice president.

It was well into the 1968 campaign. Abba Eban, the ever-proper Israeli foreign minister, was in the Oval Office and he asked Johnson about the differences between the candidates, Hubert Humphrey and Richard Nixon. To Eban's ultimate chagrin, Johnson did just that.

"Well, Nixon's got it here," Johnson said, tapping his head. "But he doesn't have it here," and he thumped himself over the heart.

"Now, Hubert has it here," Johnson continued, again tapping his head. "And Hubert has it here," tapping his heart. "But he doesn't have it here" -- and Johnson suddenly startled Eban by lunging forward and making a presidential grab for the lower reaches of the Israeli diplomat's trunk.

There are those, over the years who have made a similar (though less flamboyant) assessment of Humphrey's protege, Mondale. For the fact is that Fritz Mondale is a cautious man. His whole career has been played that way. He got to be attorney general in Minnesota by first being appointed to it, and he got to be a U.S. senator by first being appointed to it. And when it came time to decide about running for president in 1976, he took some early soundings and opted out, saying he just didn't want it bad enough to spend a year living in Holiday Inns. (Mondale was at 2 percent in the Gallup at that time in 1975, which was not as high as some, but which was higher than an ex-Georgia governor named Jimmy Carter, who was so low he was off the charts.)

So Fritz Mondale is a cautious man. And in fact, some have said it more graphically. In 1974, one journalist wrote, news that Mondale had his appendix removed "caused some [Minnesota] Democrats to say they hoped the surgeon inserted some guts before sewing him up." The author of that piece was Albert Eisele, then highly respected as a Washington correspondent and now highly respected as Mondale's press secretary. Mondale likes to explain that he had an ulterior motive in hiring Eisele: "I just wanted to take him out of journalism."

THE NATURE of the man and the nature of the job assured that Mondale would start slowly, cautiously, as vice president. Consider the beginning. The Carter White House, populated by people new to Washington, was floundering. It was operating, at Carter's insistence, without a chief of staff. Hamilton Jordan and Jody Powell and Frank Moore were stretched in all directions at once, trying to learn the conventions of the company town and meet every payroll, with staffs that were only of mid-caliber and little experience; the assembly line was often breaking down and Edsels were falling through the cracks. It was not all that good.

But Mondale was careful not to offend.

"He was cautious," says a Mondale assistant. "He did not want to push himself into the business of others. He did not want to tick them off."

"Fritz was cautious," says another Mondale assistant. "I don't think he thought it was his role to weigh in on matters of staff and structure. That was up to the president."

"At the outset, he was cautious about criticizing Ham or Jody or Frank..." says a third. "I mean, he knew well that one reason vice presidents got chopped off at the knees was that they were looked on as a threat to the president's top staff people. Look at how Rockefeller fought with Don Rumsfeld [Ford's first chief of staff], and look where it got him. Nobody over there -- not Ham or Jody or the rest -- has ever felt threatened by Fritz."

In harmony with the others is the view of Mondale on Mondale. "There's always a shakedown period," Mondale says. "I would say, frankly, I was reluctant to draw quick judgments on anyone... I mean, a president's staff can be a decisive factor to a vice president. Look at Rockefeller. I talked with him and, jeez, he was bitter -- not about Ford, but the people over here. And remember poor Humphrey. The Johnson staff really worked him over. [There were stories about how Johnson would refuse Humphrey's requests for the use of a government airplane; and how Johnson aides would keep Humphrey waiting in their outer offices, once for as long as an hour.] Hubert felt just awful about it. He too was very bitter."

Gradually, tactuflly, Fritz Mondale drew into the fray. There were the calls from senators who were complaining. Fritz Hollings, Democrat of South Carolina, did not like the way Strom Thurmond, Republican of South Carolina, was getting to make the announcements of federal grants he did not even know were being awarded and the way nobody knew when federal officials were going down to his state to speak. Jim Sasser of Tennessee did not like being the last to know about HUD grants in his state, and job appointments for Tennesseans. And so on. So Mondale talked with Frank Moore and others, and then at the urging of Carter, he assumed the role of Mister Tough Guy at a couple of Cabinet meetings warning the department secretaries to get their acts together. Carter asked Mondale to be more forthcoming -- more critical -- in his advice.

ONE EARLY Mondale role involved the overseeing of African policies. In the course of that, he met with South Africa's Prime Minister Vorster to lay out the U.S. policy line. And in the course of that, in answer to the last question in a press conference in Vienna, Mondale sazid that the U.S. policy was that South Africa should conduct elections on the principle of one man, one vote.

The South African government exploded in anger. It said it would do no more business with Mondale; and the vice president has in fact not gotten involved in African policy much since then. Mondale says he had planned to move on to other duties anyway; but he adds, "I think I did speak inartfully in that one."

Mondale later played a pivotal role in urging Carter to abandon his first-year crusade against water projects and to compromise with the angered senators and congressmen. Carter has told several people that he now views that first-year compromise as a mistake. But there are others on his staff who say that if there had been no compromise, the administration's legislative program would have wound up in a shambles, something that was just narrowly avoided, as it was.

There are other examples of where Fritz Mondale made a significant difference in administration policy -- and again, the source on this is President Carter.

"The most notable example -- which might be surprising -- was on the veto of the defense authorization bill," Carter says in his telephone interview. "Almost every one of my closest advisers recommended strongly against the veto of the nuclear carrier... All of my advisers were coming in privately to advise me not to take on Congress on tis... Ham, Stu [Eizenstat], Frank, jody and others were opposed."

But, Carter says, Fritz Mondale dissented. Strongly, but, as always, privately. Unlike past presidents, Carter is anxious to promote the importance of his vice president. It is almost as if he is padding the part. At one point, Carter's soft, conversational telephone voice becomes even softer, as he says with deacon-like reverence:

"Fritz's courageous, almost lonely stance was very pursuasive. He said it was the right thing to do, to veto the carrier. And he said that because of that it would be politically advantageous in the long run, even if we did suffer an override of the veto. His confidence was based on merit and principle."

When the White House mounted its campaign to convince the public and the Congress that the unusual veto of a military authorization bill was right, the entire White House senior staff was mobilized into a task force -- and the chairman of it was Mondale's chief aide, Richard Moe. A vice presidential aide presiding over the efforts of top presidential aides -- it is something that just did not happen in past White Houses. The mind boggles at the thought of an Agnew aide directing H. R. Haldeman, John Ehrlichman and Henry Kissinger; of a Humphrey aide giving orders to Marvin Waston, Jack Valenti and Joe Califano.

The examples of Mondale's impact that Carter has provided -- on the Middle East and the defense veto -- will no doubt prove helpful to the vice president in bolstering his image with the Jews and the liberals, groups that once considered him their closeally but who have known periods of disenchantment with Mondale in the first half of the Carter-Mondale term.

But there is little that Carter or anyone else can do to mend the growing coolness that has developed betwen Mondale and his onetime close friends and allies in organized labor.

MONDALE ASSISTANTS are fond of telling reporters how one of the vice president's greatest assets is that he serves as an administration pipeline to old labor friends. They all cite, for example, Lane Kirkland of the AFL-CIO, whom they say Mondale sees all the time. But over at the gray stone palace of the AFL, Kirkland says this is news to him. Haven't even heard from Mondale since Sept. 11, Kirkland says, and that was just when Mondale gave a speech to a labor group. It is Washington's worst-kept secret that Jimmy Carter and George Meany have no use for each other; the thing has gotten down to name-calling in the press. So Mondale has not seen Kirkland. Cautious.

The labor men are unhappy that Mondale has shown no visible means of support for their efforts to influence the Carter economic policies and that he has not been forceful in the name of such shelved promisses as national health insurance.

One of Washington's most influential labor officials recalls how union leaders walked out of a meeting with Mondale about a year ago -- "literally shaking our heads in frusttration." They had just heard their old friend give them all the arguments why health insurance had to be delayed.

"He's like all the rest of the vice presidents," says one of the labor officials. "We thought with Fritz it might be different. But it's not. We thought at first that we'd be able to go to Mondale and gain his help in arguing our case on the inside. But instead of being an advocate inside for his old friends, he's turned into an advocate for the administration to his old friends."

But not all labor officials are disenchanted with Mondale's role as a power within. That is because some of them did not expect much in the first place. "I was never enchanted with the post of vice president as a locus of influence," says one of the town's big name labor officials. "If a vice president wants to have duties, he's got to please the president -- and that's just what Fritz has done. The vice president is just a good soldier, once again."

Mondale is aware of the rap. When the latest labor litany is recited to him, in fact, it touches off the only defensive speech of what was othewise a relaxed interview in his office (an interview, by the way, that was interrupted once when Brzezinski popped in). "I have not abandoned my beliefs," he says, and he sits bolt upright in his chair and the beginnings of wattles commence to quiver, and one can almost see and hear Hubert Humphrey, talking of himself as he so often did in his third-person singular way, "Hubert Humphrey has not abandoned his beliefs ..."

BELIEFS. It is one of those things that a vice president just cannot go around exposing too often in public. "Fritz is very cautious not to project himself to the public as being in contention with me," says the president. "And I think that's appropriate. My wife has the same basic attitude toward the public. She believes that it's better for her and me to thrash out our differences privately, even on political affairs, than it is for her to go to the news media and say, 'Jimmy and I disagree on this.'"

Carter has eliminated one role of the vice presidency that past presidents have frequently put to use. He has decided not to dangle his vice president as a foil for campaign fodder. So it was that a couple of weeks ago, after a newspaper column speculated that Mondale might be dropped from a Carter ticket in 1980, the president told reporters that Mondale would be his running mate if he himself decides to run. (Remember Eisenhower, in the reelection year 1956, maintaining that it was up to the Republican convention to decide if Nixon should be on the ticket. And Nixon's coyness about Agnew in 1972. And the way Ford let Rockefeller twist slowly, slowly in the wind.)

Carter's announcement on Mondale's fate -- a full two years before the next election -- was news to many, including Mondale. The vice president was baking his way through a Virgin Islands vacation when he learned of his future by reading it in a newspaper. He had never even talked to Carter about 1980.

"When I got back to Washington, I walked into his office and thanked him," Mondale says. He pauses. "It seemed the thing to do."

Jimmy Carter and Fritz Mondale have put together a five presidency that has made this occupant more ready than most and more influential than many. It does not change the basic fact that the vice president is just the vice president, a mixture of presidential understudy and good soldier. But at least now there exists, for the first time in a long time, a partner relationship between the man in the Oval Office and the man in the wings -- a bond strong enough, even, to permit a vice president to pull a president away from an evening of Lee Marvin's singing.