In the sense that counts -- or ought to count -- at this stage of the game, Alan Cranston is a serious candidate for president. The senior senator from California, who announced his bid for the Democratic nomination last week, is a proven vote-getter in the largest state in the nation. He is an accomplished fund-raiser and capable political organizer, a man with a clear and long-established record on major issues and one who has earned the good judgment of his political peers.

He is also a man with a passion to solve one of the major challenges facing not just this country but the world: the threat of nuclear arms. And he has reached the point in his life where his energy is likely to be focused on what he has set as his overriding goal: nuclear disarmament.

If all these assets are demonstrable--as I think they are--then they may weigh in the balance against Cranston's demonstrable liabilities: he is nowhere in the polls, compared with such well-established Democrats as Walter F. Mondale and John Glenn. And he has a bald, bony head that is unmistakably out of fashion in a television age of presidential politics.

Those advantages may weigh in the balance, but then again, they may not. The other day, a top-notch Democratic Party professional, speaking of the Cranston candidacy, asked, in a tone of total skepticism, "Do you think Ronald Reagan could get elected if he looked his age? I don't. And Cranston looks older than Reagan."

That is a fact. It is also a fact that he is, at 68, closer to Reagan's age than anyone else in the race. And it is also a fact that he works a longer day than Reagan, by far, and carries without fatigue a heavier workload than most of the other Democratic contenders--including those who have a 10- or 20-year advantage on their side.

Thus, the Cranston candidacy provides an interesting test case of competence vs. cosmetics in the current political system. It is in part, at least, a test for those of us in the press who know this man well from his work as a senator and, in some cases, from his career in California politics before he came to Washington.

Here are some of the things I know about him: he was a founder of the California Democratic Clubs, one of the healthiest early blooms of volunteer party activity spawned by the Adlai Stevenson campaigns of the 1950s--one of the forces that transformed California into a two- party state. He was an honest state controller who used that office, in legitimate ways, to build a very effective statewide political organization.

Through that organization, through his energetic campaigning, through his capacity to raise money (again, without the hint of scandal), he won three terms in the U.S. Senate--twice winning in years (1968 and 1980) when California Republican presidential candidates were providing coattails for his opponents.

He has one of the best staffs in the Senate, and he works at his job as hard as any member of that body. He is an institutional man, finding power in the places where the insiders do their work--not in headline-grabbing. He became the deputy leader of the Democrats, the whip, in large part because he is one of the few liberals in that body willing to do the hard work of coalition-building.

He can count, as the professionals say. He knows who is for a bill or against it--and why. He does not kid himself, or the press, on those counts. Working under Sen. Robert Byrd of West Virginia, who felt certain ideological and political pressures peculiar to himself and his 1982 reelection campaign, Cranston became the de facto leader of the Senate Democrats on many issues during the past two years.

Thus far, I think almost anyone in the Senate and around the Senate would endorse the view of Cranston that I have summarized. Beyond that, colleagues and correspondents would split all over the lot in their judgments about him and, particularly, in answering the question whether he has the extra dimensions of wisdom, eloquence and leadership that one ideally seeks in a president.

In 1981, when a few others said no, Cranston said yes on final passage of the Reagan tax-cut package. That is a judgment for which he can be held to account. His advocacy of arms control is so fervent that some may question whether he would be as effective--and tough-- a bargainer as you would want sitting down with Yuri Andropov.

But these are substantive questions of judgment and temperament, which the voters can decide in their good time. All I am saying is that Alan Cranston is a serious, capable, mature and tested politician--the kind of man who ought to be running for president. And it will be a damned shame if he is given short shrift because his head is bald or his polls, at this point, are low.