WHEN IT COMES to the matter of strong opposition to any and all increases in non-defense federal spending, Ronald Reagan is no Johnny-come-lately. For as long as many voters can remember, Mr. Reagan has been an outspoken, frequently even eloquent, nemesis of Washington's big spenders. Mr. Reagan's objections to the public financing provisions of the election reform act probably did not surprise many familiar with his career.

In pursuing the 1976 Republican presidential nomination, Mr. Regan was required by circumstances to suspend temporarily his personal objection to that law and accept some limited matching funds from the U.S. Treasury. The federal checks to Mr. Reagan for that 1976 campaign added up to about $4.5 million. For the 1980 campaign, Mr. Reagan arranged to accept some limited federal assistance. In the pre-convention period, his campaign submitted vouchers for and had certified by the Federal Election Commission public payments in the amount of $7,294,461.55.

Once he had won this year's Republican presidential nomination, Mr. Reagan applied on July 18, as he was entitled to do under the election law, for the general election subsidy of $29,440,000. So over the past four years he has managed, in all, to accept and cash government checks totaling $41,212,230.22.

Before Mr. Reagan and his running mate, George Bush, received the 1980 general election check, they had to fill out a form. The form contained this language as a condition for their receiving the public check: "No contributions have been or will be accepted by us or by our authorized committees." As far as anyone knows, no checks beside the government check have been deposited in the Reagan-Bush account.

Still, in October 1980, the Republican presidential campaign is benefiting from one of the most conspiratorial hoaxes and counterfeit schemes ever seen in American politics. We respect Mr. Reagan's right to oppose the public financing features of the election law, all the time availing himself and his campaign of them. But to remain silent while the synthetic "independent expenditure" committees, headed by such Reagan stalwarts as Sens. Jesse Helms and Harrison Schmitt, create and produce radio and television commercials and then buy very expensive air time is disingenuous.

Mr. Reagan and his campaign managers know that broadcast advertising is being produced and purchased by people whom they also know, outside their campaign. Now is the time for Messrs. Reagan and Bush, in spite of any personal reservations they might still hold about the election reform act, to tell their friends and supporters to cease and desist -- to tell them and the voters that they are willing to try to win this campaign without bending or bruising the law.