What has happened here in Orange County reminds us again that nearly everything in American politics can eventually be reduced to numbers. Consider the case of "liberal" Massachusetts, which, between 1926 and 1974, went from being one of the most reliably Republican states to one of the most reliably Democratic.

Some credit for that conversion must certainly be given to such Democratic leaders as Al Smith, Franklin Roosevelt and John Kennedy. But the principal cause of the realignment of the Bay State took place in Massachusetts maternity wards, where Catholic parents, especially Irish, were having a lot more little Democrats than Yankee Protestants were having little Republicans. Political change comes in a number of forms.

That maxim is especially evident here in California, where both change and growth have been relentlessly constant. This state's fascinating politics can perhaps best be understood as the tale of two counties: Orange County in the south and Marin County north of San Francisco.

Both places have been lampooned and satirized as cultural opposites: Marin, the fiscally conservative but culturally hip and permissive hot tub capital; Orange, the headquarters office of America's right-wing fringe for nearly 30 years.

Both caricatures are overdrawn. It is possible that the next trendy drink in Marin may well be Perrier Light, and Orange County was, in fact, Ronald Reagan's best in the nation in 1980. But both counties are wealthier and better educated than prosperous and educated California. It's just that while Marin was growing 8 percent in the 1970s, Orange was growing five times as fast.

Votes are numbers that reveal something about the people who cast them. While losing the county, Jimmy Carter actually ran better in Marin against Ronald Reagan than he had against Gerald Ford, but not as well either time as George McGovern ran there against Richard Nixon. Marin voters were comfortable with Gerry Ford, who, it will be recalled, supported ERA and did not teach Sunday school.

Four hundred miles and several life styles away from Marin is Orange County, where Barry Goldwater won his biggest, and one of his very few, California pluralities. Two features are remarkable about the numbers from Orange County: the consistency of its Republican voting and the consistency of its population growth.

In 1960, Orange County was home to 700,000 people, and that was five times as large as Marin. Since then Orange has tripled its size and is now eight times more populous than Marin.

That growth is apparent in the election returns. In three-way presidential races, the county gave Richard Nixon in 1968 and Ronald Reagan in 1980 better than six out of 10 of its votes. But Reagan's margin, just 12 years later, was nearly 200,000 votes larger than Nixon's.

In the politics of 1984, the growth -- and the numbers -- can be found in places that vote more like Orange County than Marin County. Over half the population of the state of California, Florida, Arizona, Alaska, Colorado, Wyoming, Oregon, Washington, Idaho and New Hampshire were born some place outside those states.

These are not accidentally among the fastest growing and, in presidential elections, most Republican states in the nation. Since 1968, only one of these states -- Florida in 1976 -- has voted for a Democratic presidential nominee.

The growth in American politics in 1984 is to be found not in the Marin counties, but in the Orange counties. That's just one more reason for GOP optimism.