NOT TOO MANY elections ago, running for president was considered the best preparation for, being president. The successful candidate had to seek and win support in all sections of the country, respond to real voters' questions, and learn something about the United States and a lot about himself in the process. The very qualities generally required to do well in a presidential nomination fight -- stamina, judgement, intelligence, leadership -- are all valuable qualities in a chief executive.

Next year, with 36 primaries in just 14 weeks, even the most dedicated advocate of the value of baptism by fire would be hard pressed to defend the new political decathlon posing as a nominating process. But if you think that winning three dozen separate elections is all that would-be presidents have to worry about, consider the pitfalls of campaign spending.

Proper acknowledgment has never been made of the contribution made by W. Clement Stone to the way the United States now finances presidential campaigns. Mr. Stone, a very successful Chicago businessman, gave the 1972 Nixon campaign over $1 million of the $61 million raised by that winning campaign. After learning what some of the individuals in that campaign did with some of that $61 million, the 93rd Congress enacted the Federal Election Reform Act of 1974.

Individual contributions are now by law, limited to a maximum of $1,100. A presidential candidate who raises $5,000 in individual contributions of $250 or less in 20 different states is then eligible for federal matching funds for all contributions up to $250. In 1976, in the preconvention period, fully 36 percent of all the campaign funds received by major candidates came from public matching funds. But like all federal programs, there's a hitch for the candidates who accept public funds. Each candidate must abide by state spending limits (from $264,600 in New Hampshire to $3.4 million in California) and an overall spending limit of $13.2 million in the campaign for the nomination.

One irony of the act -- which had as its overriding objective to diminish the influence of money in presidential campaigns -- is that nowadays people become "serious" candidates not by demonstrating political support, but by proving their prowess as fund-raisers. Money, its raising and careful management, is as important as ever in presidential politics.

In fact, every candidate in 1980 will confront the budget dilemma of what we like to think of as the Conscientious Republican Presidential Hopeful Our C.R.P.H. knows that to be taken seriously at the Detroit convention, he will have to demonstrate strength in all regions of the country. So he decides to skip the state conventions and concentrate only on the 36 Republican primaries. Beginning in New Hampshire on Feb. 26, he campaigns only in those places that hold primaries and spends only what the law allows in each place. Not a cent more.

But, alas, the C.R.P.H. will be in serious need of our sympathy and competent legal defense counsel before only the 15th primary in Texas on May 3, because his spending will have exceeded the overall limit of $13.2 million by some $800.00. So with 21 primaries still remaining in such politically significant jurisdictions as Michigan, Ohio, Oregon, California and New Jersey (not to mention the District of Columbia), he finds himself out of money and outside the law.

The proliferation of primaries, of course, has contributed to this "political Proposition 13," simply because there are more of them in a shorter period and they are more expensive.

Rep. Richard Cheney, who as an aide to President Ford saw this problem up close, wisely observed that a candidate's campaigning under the present law and present system may mean he is "better equipped to serve as director of the Office of Management and Budget than as president."