YESTERDAY FORMER Texas governor John B. Connally became the first presidential candidate in the last two national campaigns to forgo public matching funds. Mr. Connally, who leads all candidates in both parties in privately raising campaign funds, explained his decision in terms of both principle and politics: his long-held opposition to the principle of public financing of campaigns, and the frank admission that he was trailing Ronald Reagan in the fight for the Republican presidential nomination.

As is often the case when principle and politics are co-authors of an decision, here it is the politics that is more interesting. Mr. Connally has succeeded in raising more than $7 million for his campaign, but failed at the same time to raise his numbers in the Harris and Gallup polls. By federal law, all presidential candidates who accept matching public funds are now limited to primary campaign spending limits of $264,000 in New Hampshire, $435,000 in Iowa, $1,351,000 in Florida. Florida is most probably the crucial factor in the non-principle, political aspect of Mr. Connally's decision. You will recall that last month Florida Republicans held their first quadrennial non-binding straw balloting among presidential candidates. The Connally campaign, in a cost-benefit ratio that would make the Army Corps of Engineers blush, spent in the neighborhood of $350,000 to win just 354 straw ballots (and was in second place to the same Mr. Reagan). Even allowing for Democratic inflation, that worked out to about $998.70 per Connally vote. If, as is expected, that November expenditure will be deducted from the March spending limit in Florida, Mr. Connally would have placed himself at a serious competitive disadvantage against Messrs. Reagan, Bush, Baker, Crane, Dole et al.

There is an old political maxim that urges every candidate to do that which the candidate does well: if the candidate is a good speaker, get him before a crowd; if the candidate is charming in personal meetings, get him out with the folks. Mr. Connally obviously raises campaign funds exceptionally well. His supporters make much of his going through various corporate headquarters like a human Electrolux -- picking up lucre instead of lint. In just one year, John Connally has become to the Fortune 500 what George McGovern was to the Chicago 7: their favorite.

So, understandably, Mr. Connally has apparently decided to concentrate his considerable energy and persuasiveness on that task most candidates abhor, soliciting campaign contributions. The Connally campaign will no longer be bothered by any statutory limit on campaign spending in New Hampshire or elsewhere. The only Connally campaign limit will be that imposed by the candidate's time and effectiveness in collecting private contributions.

Somehow it strikes us as proper that John Connally, a convert to the party that has proudly trumpeted free enterprise, has become the first post-Watergate presidential candidate to run a true free-enterprise campaign. Just maybe John Connally had been perusing the collected works of the late Will Rogers, who observed: "Politics has got so expensive it takes a lot of money to even get beat with."