It is a tribute to Sen. Alan Cranston's respect for the substance of American politics that he has made the survival of mankind in the nuclear age the central issue of his bid for the Democratic presidential nomination.

It is a tribute to his respect for the trivialities of American politics and his hunger for the White House that Cranston, a man with little regard for his personal appearance, has dyed his hair, rubbed tanning oil on his face, gained 10 pounds and taken speech lessons since announcing as a candidate.

This may sound like unusual behavior for a respected Senate insider who has made his candidacy an idealistic crusade against nuclear war. But those who know Alan MacGregor Cranston best see nothing unusual in it. They regard him first and foremost as a pragmatist who will do what is necessary to win the presidency.

"It isn't the real Alan Cranston, but here is a guy who is willing to do what is necessary to be competitive," says Lu Haas, a former aide. "If it is absolutely necessary for him to gain 10 pounds or dye his hair, then he'll grit his teeth and say, 'Damn it, I don't like it, but I'll do it.' "

Few politicians have so few natural political assets; few have been underestimated so often. According to his detractors in Washington and Sacramento, Cranston is too old, too bald and too bland to be elected president.

But, ever pragmatic, Cranston has tried to turn this to his advantage with a self-deprecating television commercial in which he asks: "Why vote for a 69-year-old man who they say is not charismatic, who's bald?"

His answer is that a Cranston presidency would have "two clear purposes: ending the arms race and full employment. Because that's how you beat Ronald Reagan--even if you're bald."

Cranston is running a remarkably single-minded presidential campaign. None of his Democratic opponents has staked so much on a single idea, albeit one as crucial as nuclear arms control.

Cranston's world view, like those of many politicians of his generation, was shaped by events connected with World War II. He watched the rise of fascism in Europe as a young foreign correspondent, and returned home in 1939 urging U.S. intervention. He published, among other things, "Hitler's 10-year Plan for Conquest of Europe," based on propaganda pamphlets he had gathered.

But his experiences in the postwar years left him with a fundamentally different perspective of the Cold War than many of his contemporaries. He believes that the nuclear age changed the dimensions of world conflict and that the Soviet Union cannot be seen as an equivalent of Adolf Hitler.

In short, he thinks that it is possible to cut a deal with the Soviets for mutual survival.

Cranston envisions a presidency unlike any before, one completely devoted to reducing the threat of nuclear holocaust. Only one other issue, jobs, would get his personal priority.

"A president should focus his or her mind on one or two principal purposes," he said. "Otherwise, a president is overwhelmed by the demands of the moment or the crisis of the day and has no sense of direction. You squander your moment in history."

On Inauguration Day, "I'd announce that we would not test or deploy any nuclear weapons as long as the Soviet Union did not test or deploy," he said. "That same day I'd get in touch with the Soviet leader and urge that we have a very early meeting to discuss how to really halt the arms race and start dismantling our stockpiles."

A freewheeling series of summits would soon follow. "President Cranston" personally would take charge, like President Carter at Camp David. Cranston said he believes that the Soviets would respond because "I would not be seeking advantage over them, but attempting to meet our common needs."

It is revealing that many people who have known and watched Cranston over the years have given little serious thought to what kind of president he would make. Most, in fact, were surprised that he became a candidate.

"He's not a colorful guy or a hero. Alan has always been more of a plodder," said former California governor Edmund G. (Pat) Brown Sr., a longtime ally.

Supporters and detractors agree that Cranston has the experience and intellect to deal with the job. He is seen as someone who, almost to a fault, is willing to listen to all sides of an argument.

His large staff is regarded as loyal and talented.

"Cranston delegates easily," said one Senate staff worker. "In style, he would be more like Reagan than Carter as president. He doesn't get bogged down in details."

"He'd be a superb president," said a friend, Paul Ziffrin, a former Democratic national committeeman from California. "No one knows the issue like he does, he's articulate without being charismatic. He wouldn't let ego get in his way . . . . He's been talking about disarmament for years. This is a real passion for Alan. He didn't take a poll to find this is what people think."

A California journalist who has watched Cranston for 20 years concurred: "He'd be harder on the Russians than you might think. There's a basic toughness in Alan Cranston. He isn't a pacifist. He believes in power."

A California lobbyist and veteran of the state's politics disagrees:

"He's too light to be president. He doesn't have the kind of commanding presence you need for that job . . . . I think he's just indulging himself by running for president."

It is easy to ignore the complex and often contradictory forces that shape any individual. This is especially true of Cranston. He is a man of many layers, a politician hard to read, unemotional and low key. In his long and varied career he has been a champion sprinter, a foreign correspondent, an anti-Hitler propagandist, a leader of the United World Federalists movement, an author and playwright, a real estate developer and politician.

Friends and foes regard him as honest and straightforward. In the Senate, where he is minority whip, he is considered a skillful inside player and artful compromiser who can get things done. He has that most valued of Washington attributes: clout.

On the surface, he is uncommonly deceptive.

Take such a basic matter as his physical appearance. Though sometimes described as "cadaverous looking" because of his tall, lean frame and bony features, Cranston runs daily (he once held the over 55 record for the 100-yard dash) and watches his diet religiously.

Doctors at Bethesda Naval Hospital declared him "exceptionally healthy" after recent exploratory surgery when they were alarmed by scar tissue on a lung. It turned out that Cranston had pleurisy.

His name is synonymous with such liberal causes as civil rights, the environment and the nuclear freeze. The liberal Americans for Democratic Action give him a lifetime voting record rating of 85, second only to Walter F. Mondale among the Democratic contenders. He has been endorsed by the United Farm Workers Union and the California chapter of the National Organization for Women.

Yet Cranston is a friend of the banking, independent oil, aerospace, agribusiness and movie interests that are so powerful in his home state.

"He's a good politician in that he takes care of all the interest groups. He's been very good about being accessible. Even when we don't get his vote, he makes sure we see the right people and that our case gets a hearing," said Robert Monagan, president of the California Manufacturers' Association. "California manufacturers have a great many concerns in Washington, and Cranston has been very, very helpful."

For a candidate considered so bland, Cranston has had an unusually successful and exotic career. Son of a wealthy real estate developer, he grew up in Los Altos, a suburb of San Francisco in what is now called the Silicon Valley. The Cranston estate, called Villa Warec, was a large, genteel place with a swimming pool, orchard, waterfall and servants.

Though his father briefly faced bankruptcy during the Depression, Cranston was a child of privilege.

As a youth, he was mischievous, bookish and somewhat shy, his sister, Eleanor Fowle, wrote in a biography of him. "You never could tell very much about what was going on behind the freckles and the large, dark eyes," she said.

Two early influences were noteworthy:

Athletics. Cranston was a champion high school and college sprinter. At age 69, he continues to run daily, sprinting down hotel corridors on the campaign trail, and religiously recording his times. "Track gave him his first self-confidence and released him from his uncertainties about himself," his sister wrote.

His father. William Cranston was a Republican with a strong distrust of Franklin D. Roosevelt, but he had an eclectic circle of friends, including muckraker Lincoln Steffens and Fremont Older, a crusading editor. Cranston's fascination with politics and journalism grew over dinner-table conversation. His father, despite success in real estate, "always wanted a more prestigious occupation," Cranston says.

Cranston eventually went into his father's real estate business, which gave the young man a financial base with which to pursue his political career. But his goal, Cranston says, was to become a foreign correspondent.

After he was graduated from Stanford in 1936, Cranston went to Europe as the events leading to World War II were unfolding.

He wrote about the 1936 Olympic Games and watched the rise of fascism in Italy as a $12.50-a-week reporter for the Hearst-owned International News Service. As the first American reporter in Ethiopia after the Italian conquest, he was sued for libel by Haile Selassie for writing that the emperor had a nephew sawed in half. Selassie won the libel suit.

He returned to the United States, Cranston says, determined to change events, not write about them. He focused on Hitler. Noticing that the version of Hitler's "Mein Kampf" selling in the United States omitted scores of ugly passages, Cranston and a friend published an unabridged version of the book with commentary.

Half a million copies were sold at 10 cents each before Hitler's publishers sued for copyright violation, which gives Cranston the basis for the claim that he is the only presidential candidate ever to be successfully sued by the heads of two foreign governments.

Tenacity has been the hallmark of Cranston's political career. "It isn't anything spectacular that he's done. People just like him," said former governor Pat Brown. "He's been good and he's been lucky. He has also picked his shots very carefully."

Cranston's base was the California Democratic Council (CDC), a network of reform-minded political clubs forged in the early 1950s, when the Democratic Party had all but disappeared as a force in the state.

As founding president, Cranston crisscrossed the state, building the CDC into a political power, and got himself elected state controller in 1958, at the age of 44.

Cranston the officeholder was somewhat of a surprise to his old liberal friends.

As controller, Cranston inherited California's second-largest statewide patronage operation, a network of 134 inheritance tax appraisers. As leader of his party's liberal wing, Cranston was expected by some to dismantle the patronage system. Cranston didn't. Instead, he hired 15 more appraisers.

If this showed Cranston as a hardball politician, a darker side emerged in an incident first reported by Carl Cannon of the Knight-Ridder news service last fall. According to Tom Braden, the liberal newspaper columnist and then editor of the Oceanside Blade-Tribune, Cranston approached him in 1964 with a sexually explicit, highly compromising photograph of a potential Democratic opponent.

Braden was reluctant to discuss the matter, but when told that Cranston had completely denied it, he said: "How could I make that up? It's the kind of thing you don't forget . . . . I thought it was pretty shoddy business. It certainly changed my opinion of the man," meaning Cranston.

By luck or design, Cranston the senator has been blessed with weak opponents from the right wing of the Republican Party. "Alan . . . works very hard to have shoo-in elections," said Democrat Kenneth Cory, the current California controller. "He works the phones seven days a week, 52 weeks a year. He works not only his friends, but neutrals and his enemies."

One example of Cranston's style occurred in 1973, when President Nixon nominated Rep. Gerald R. Ford (R-Mich.) as vice president after the resignation of Vice President Spiro T. Agnew.

Cranston, saying he was unsure whether to vote to confirm Ford, sought the advice of hundreds of Californians. He telephoned every California delegate to the 1972 Republican National Convention. Later, during the confirmation debate, Democrat Cranston was lavish in his praise of Republican Ford.

Cranston won reelection the next year with 61 percent of the vote, including the support of many Republicans. In 1980 he won with a record 1.7 million votes.CC ranston, however, has suffered two political losses. The first was in the 1964 C Senate primary to Pierre Salinger, President Kennedy's press secretary, who called Cranston "the eager tax collector who'd make a fine mortician."

His second defeat, in the 1966 controller's race, was a pivotal event in his maturing as a politician.

The defeat caught Cranston, then the state's leading liberal Democrat, by surprise. He was supposed to have been a shoo-in. His Republican opponent, Houston Flournoy, entered the race almost as a lark after a late-night poker game in which his friends agreed to put up the filing fee.

Cranston was so confident that he spent much of the fall campaigning against the Republican gubernatorial nominee, Ronald Reagan. He prepared a 26-page white paper on the right-wing John Birch Society, and called on Reagan to disavow Birch society support. But when the votes were counted, Cranston and Pat Brown were buried under a Republican landslide.

The post-1966 Cranston became a more cautious, less ideological politician. He avoided high-risk battles, became leery of intraparty fights and sought compromise and accommodation. He made peace with his long-time party rival, Jesse Unruh, then the powerful speaker of the California Assembly and now state treasurer.

The day after he was defeated as controller, Cranston told a startled news conference that he was considering a run in 1968 for the U.S. Senate because "conservative GOP elements that have elected Reagan will try to wipe out Sen. Thomas H. Kuchel R-Calif. , a moderate. Kuchel might be defeated in the 1968 primary by the right-wing Max Rafferty . . . ."

Cranston was right. Rafferty, a glib state superintendent of public instruction, upset Kuchel in the Republican primary.

Cranston ran that year as a middle-of-the-road candidate. He spoke out against the Vietnam war, but refused to disavow President Johnson or endorse the antiwar candidacies of Sens. Eugene McCarthy (D-Minn.) or Robert F. Kennedy (D-N.Y.). He stayed away from the Democratic National Convention in Chicago because he said he knew it would be divisive.

Cranston won the Senate race after it was revealed that Rafferty, a staunch supporter of the Vietnam war, had sat out World War II with an alleged leg injury and then threw his crutches away after VJ Day.

Caution was the keynote of the newly elected senator. Despite his longtime global concerns, he didn't seek a seat on the Foreign Relations Committee until he'd been in office 12 years. His explanation is revealing:

"I had observed that committee was not good as a political base. You can't do much for your constituents there, and you create vulnerabilities. Witness what happened to Frank Church," an Idaho Democrat and committee chairman who was defeated in 1980.

"I selected three committees that I thought would help politically: the Labor Committee, which got me into basic social issues like education, health and the troubles of working men and women, the more or less liberal concerns; the Banking Committee, to help me deal with the business constituency of California, and the Veterans' Committee, as an offset of my dove-like image."

Cranston cast predictable liberal votes, but showed a knack for building personal relationships with ideological opposites such as Sen. Russell B. Long (D-La.).

That came through in his handling of California business interests.

"Alan works the business community one on one. He tries to figure out an area where he has an agreement," said California Controller Cory. "The practical politics was that he had a limousine-liberal base in L.A. and realized that wasn't enough. After he became a senator he went out of his way to dispel the image that he was some kind of left-wing flake."

His reputation as a tenacious worker and skillful vote counter was built on his efforts in behalf of the Lockheed Corp., a home-state industry. As the Senate began voting on a federally guaranteed bank loan for the aerospace firm, Cranston recalled that he quietly told Sen. Lee Metcalf (D-Mont.) that he held the deciding vote and would determine whether "30,000 Lockheed workers would be thrown out of work." The measure passed by a margin of one vote, Metcalf's.

But nothing about Cranston has upset liberals more than his repeated votes for the controversial B1 bomber, which would be built in California. He argues that the B1 is needed to help maintain the United States' nuclear deterrence system because the B52, which it would replace, is outdated.

"Besides, I support the nuclear freeze, which would stop the B1 totally," he adds.

It was Cranston's willingness to work quietly behind the scenes, not his ideology or personality, that made him a leader in the Senate.

Early in his Senate career he bridged a gap in the Senate Democratic leadership between then-Majority Leader Mike Mansfield (D-Mont.), a liberal reluctant to twist arms, and Majority Whip Robert C. Byrd (D-W.Va.), a moderate conservative. Cranston gradually became a conduit for restless liberals and became one of the Senate's leading fund-raisers, generating millions for his colleagues' campaigns.

Whatever his deviations on other issues, Cranston's commitment to arms control has been unwavering. In 1977 he led the confirmation effort for President Carter's controversial arms control negotiator, Paul C. Warnke. The following year Cranston was an undisputed Senate leader in developing support for the then-pending SALT II arms limitation treaty.

His roots in the arms control movement go back to a conference in Dublin, N.H., in October, 1945, that gave birth to the United World Federalists (UWF), an ill-fated crusade for peace through world law by people who believed that the world was on the verge of an uncontrollable and catastrophic nuclear arms race and that nuclear holocaust could be prevented only by organizing a world government with "limited but adequate" powers.

Cranston spent most of World War II in Washington, first as a junior executive in the Office of War Information, then as an enlisted man writing for "Army Talk." He apparently was invited to the conference because his book, "The Killing of the Peace," was named one of the 10 best of 1945 by The New York Times.

He spent much of the next six years, including three years as president of UWF, preaching around the country that only through disarmament with "an international army and a world court" could there be world peace.

In retrospect, the idea seems revolutionary, but Saturday Review editor Norman Cousins insists that it "was not visionary then."

Among the members of UWF's Los Angeles chapter was Ronald Reagan.LL ooking at his long and varied public career, there often appear to be two different L Alan Cranstons. The first is the brash, young adventurer and passionate idealist, the daring young man who went to Europe to become a foreign correspondent before World War II and became a champion of "One Worldism" after the war. This is the presidential candidate who has made the bold gamble that a campaign built around arms control and a nuclear freeze can make him president.

The second Cranston is a tactician given to caution and compromise, a survivor.

The presidential candidate often appears to be more the first Cranston than the second.

"Reagan radicalized Alan Cranston," one longtime Cranston observer said. "He felt Reagan would be a disaster for the country. He felt Reagan was at the vanguard of a radical right-wing menace and was dangerous for the country."

Supporters of this theory note that, while other Democrats ran for cover in the first year of the Reagan administration, Cranston picked up the anti-Reagan banner on a wide range of domestic and foreign policy issues. Some believe he wouldn't be running this year if Reagan weren't president.

He voted against the confirmation of James G. Watt as interior secretary and attacked the administration's tax program as inflationary and favoring the wealthy.

But the question remains: who is the real Alan Cranston?

His answer: "When you're effective you don't have any rigid lines."