It is spring-training time in Brooklyn, and the phenom is taking batting practice, smacking line drives off the fences. Mario Cuomo is a former minor-league centerfielder, currently is a major-league governor and (according to the boys in the press box) is a can't- miss candidate for the politician's Cooperstown.

Today he is in the Brooklyn Supreme Court building, seated beneath a sign that says "Vox Populi." Evidently Latin is big in Brooklyn. Cuomo certainly is.

He is taking questions from the bleachers and the natives are not restless. The questions are what baseball people call meatballs -- soft tosses grooved over the heart of the plate, letters-high. Such questions ("I want to begin by thanking yu, governor, for all you have done for . . .") do not give Cuomo a chance to be impressive, but the questions say something impressive about his governance.

Ebbets Field, home of the Brooklyn Dodgers before Los Angeles' larceny, was never a garden of shrinking violets. Brooklynites, even more than normal New Yorkers, are vocal about their grievances. But the only serious grievance voiced in 2 1/2 hours of Cuomo's open meeting is that Brooklyn deserves a new stadium and a team to romp in it.

The main argument between Cuomo and New York Republicans is how big the tax cut should be. Republicans want it bigger than Cuomo's proposal. They say he is underestimating revenues. Cuomo promises that the cut in personal income taxes is just the start of a "pattern" of cuts that will include business taxes. This, in the Peoples Republic of New York? Yep, and it is like many other states: the two most popular politicians are the president, a Republican, and the governor, a Democrat.

Cuomo came to the nation's attention at the 1984 Democratic National Convention with the keynote speech that proclaimed: "We can do it again." The antecedent of the pronoun "it" was approximately this: We can use energetic government to engineer a more egalitarian society.

But William Schneider, a fellow at the American Enterprise Institute, understands the Democrats' problem. Their ambitious social agenda depends, he says, on sustained and rapid economic growth to produce the economic surplus for egalitarian social engineering. However, such growth dilutes the sense of urgency for redistributive policies.

It is possible that -- God and national journalism willing -- Americans can come to find governors interesting. Governors have many more direct responsibilities than legislators have, and inevitably have more interesting records. It is hard to be ideologically monochrome when administering education and health systems, settling strikes and prison riots, and balancing budgets -- as governors are required to do.

Schneider notes that recent Democratic nomination contests have not been left-versus- right or young-versus-old. Rather, they have been "insiders" versus "outsiders."

The modern history (and the decline) of the party began in 1968, in Chicago. There, Hubert Humphrey (assisted by a prot,eg,e named Walter Mondale) defeated forces outside the party establishment -- actually outside the convention hall, in the streets. In 1972 and 1976, the nominations went to outsiders -- George McGovern over Ed Muskie and others, Jimmy Carter over Scoop Jackson and others. In 1984 Mondale, the insiders' revenge, defeated Gary Hart, whose new idea was that insiders are burnt-out cases.

A governor, especially of New York, is an interesting blend, being outside the federal publicity machine but inside the game of governance. But Cuomo does not give the impression of wanting a presidential nomination in the consuming way that one must want it if one is going to get it. He says that the wrong question, constantly asked, is: Are you going to run for president in 1988? The correct question is: Are you going to seek reelection in 1986? He says that if his answer to the latter is "yes" (and it almost certainly will be), then the answer to the former must be "no." It must be, because he could not, practically or properly, begin, simultaneously, a second term as governor and a presidential campaign.

He often rises early, sometimes to write his diary, and occasionally he tunes in C-Span. He watches -- can you imagine? -- reruns of congressional proceedings. Is he inoculating himself against Potomac Fever, or measuring the opposition. Whichever, he has been warned.

When a New York reporter at the Brooklyn meeting asks Cuomo about the presidency, Cuomo groans. He is required to do that. The audience also groans. This is optional and interesting. They like him where he is, and will become more like New Yorkers -- surly -- if he starts acting like a presidential candidate. When he arrived in Brooklyn for his batting practice, a female constituent semi-swooned: "You're not as ugly in person as on TV." That was a New Yorker trying to be nice.