Yoggi Berra could have been talking about the American electorate of the '60s and '70s when he said, "If de fans aren't going out to de ball park, you can't stop 'em."

In 1980, somebody or something has apparently stopped them. After years of cliches about apathetic cynical turned-off voters, political tea-leaf readers suddenly find themselves pleasantly puzzled and groping for theories to explain the stunning voter turnouts for both major parties in the early contests.

Will this honeymoon between the people and the process last until November? Or is it only a prespring fling? If it lasts, who will benefit -- the Republicans, the Democrats, or John Anderson?

Mindful that the buzz word of the month is "volatile," all the experts are urging caution in interpreting the entrails.

As President Carter's pollster Pat Caddell put it, "I'm not ready to go off the end of the bridge" with any conclusions.

But the figures are arresting. In the New Hampshire primary, for instance, 146,592 Republican and 110,758 Democratic votes were cast. That was significantly higher than the primary vote for 1976 (110,000 Republican and 81,000 Democrat) and much higher than the vote in 1968, which some consider more comparable. That was the year of assassinations, urban riots and Vietnam war clashes, the year of "Clean Gene" McCarthy -- issues and faces to match 1980. The 1968 vote was 103,938 Republican and 55,464 Democratic.

The Republicans, ravaged by Watergate and Nixon, naturally hope to benefit. And so far, the numbers and the popular wisdom about the country "turning right" seem to bear them out.

In the Iowa caucuses in January, the Republicans drew four times as many voters as they did in 1976, in Massachusetts (albeit with a heavy independent and Democratic crossover vote), they more than doubled the vote count and they set records in Minnesota, Vermont, Puerto Rico and New Hampshire, by the party's count.

The Democratic turnout, while unexpectedly high, was not as dramatic.

"There is a congruence of people sensing once again that their vote means something and being really concerned about the country," said Bill Brock, chairman of the Republican National Committee.

"I'm not sure where they'll settle" he added, "They are really questing. But they look like they are looking for a president, and not just for a winner."

Other indications seem to contradict the Republican optimism. For instance, a Washington Post poll conducted in January, based on a national sampling, suggested strongly that a lion's share of newly attentive potential voters consider themselves Democrats.

Among people under age 35 who say they have voted irregularly or not at all in the past, about half say they intend to vote this time. Pollsters allow for a "lie factor" in such claims, but these people backed up their claims in a test which showed their knowledge of the issues was higher than that of other young adults who said they have no intention of voting this time.

At the time of the poll, these potential new young voters said they considered themselves Democrats more than 3 to 1 over Republicans. Independents numbered only slightly higher than Republicans.

On social questions, the young adults who said they intend to vote were considerably more liberal than those who said they intend to sit out the election.

This could be the year that millions of previously nonvoting members of the baby-boom generation finally start going to the polls and become a significant new voting bloc, some analysts have said.

Of the 75 million Americans who have reached voting age since 1960, about 50 million have still not registered to vote, according to Republican pollster Robert M. Teeter.

"This could be the beginning" of their entry into the game, he said, "but it's too early to be sure." . . .

As to whether they'll go conservative or liberal, Teeter said "This is a very centrist country. It has rarely taken great lunges to either the right or the left. If it's moving, it's probably rightward, but that's because the movement in the '60s was slightly to the left. Frankly, we've never strayed very far from the center."

The issues change more than the people do, he said. If this year's issues were social, instead of oriented to economic and foreign policy concerns, "people would probably be sounding liberal."

A number of analysts see the throngs of voters as the product of a fleeting combination of media hype, "pinching" national crises as one put it, an intriguing horse race among candidates, and unseasonably good weather. A fluke, not necessarily a trend.

"I think we're not witnessing a tidal trend, no decline in alienation or cynicism," said Garry Orren, pollster for Sen. Edward M. Kennedy. "And we're not seeing a reflection of the health of the parties."

He attributes the turnout to combinations of elements that varied from one state to another.

In Iowa, for instance, the media, realizing they had missed something there in 1976 when Jimmy Carter emerged, "essentially camped out there for a year" and hyped the caucus into a primary.

Richard Wirthlin, pollster for Ronald Reagan, on the other hand, sees "a different electorate this time around, showing much higher interest, and maybe differently motivated."

Always in the past, the better educated and higher income people were more likely to vote. But his recent polling in New Hampshire indicated, he said, that "it was the lower to middle income high school graduates who said they were most interested. This is a group which also tends to be more Democratic."

Curtis B. Gans, of the Committee for the Study of the American Electorate, had some good news and some bad news in his speculation.

"These turnouts speak well. They show that people will turn out when they feel they are offered a decent choice, and they do want to control their destiny."

But, he added, the present party system "is very badly misaligned" and will probably deny the voters much excitement of choice in the November election.

The major new group that has come into the electorate since the 1940s, and now makes up 40 percent of it -- the suburban, white-collar professional class -- "doesn't have a real outlet for its views in either party," he said.

While a candidate such as John Anderson, with his fresh synthesis of views, might benefit from their interest, Gans noted, the popular wisdom is that he'd never make it past his own party machinery.

Thus, the parties will probably narrow the choice in the fall to Carter vs. Reagan or Ford, Gans concluded -- "not a choice that will mobilize a lot of people to the polls."