LAST THURSDAY, a U.S. Treasury check for roughly twenty-nine-and-a-half million dollars was picked up and deposited to the campaign account of Republican presidential candidate Ronald Reagan. It represents the entire federal payment to which Mr. Reagan and his campaign are entitled. But if some friends of Mr. Reagan have their way, these public funds will represent only a fraction of what is spent in his behalf over the next three months. Public financing was supposed to have been an either/or thing. Either you took the federal moolah or you raised all of your own. The Reagan company has looked at the either/or provision and replied: why not both?

How can this be done, you ask, if the Election Reform Act provides that the Republican or Democratic presidential candidate who accepts the public subsidy is then barred from accepting any additional contributions from individuals or organizations? This is how: the Supreme Court ruled in basically upholding the act in 1976 that independent groups cannot be prohibited from spending any money in support of or in opposition to a candidate so long as there is no collaboration or cooperation between the campaign and the people making these independent expenditures.

So supporters and some "friends" of Mr. Reagan, over the past few weeks, have announced the formation of groups that have the stated objective of raising and spending somewhere between $35 million and $55 million to elect him in November. They deal with the question of independence by running over it. Many of the people on the committees, in fact, including Sen. Jesse Helms of North Caolina and Sen. Harrison Schmitt of New Mexico, were active and influential supporters of Mr. Reagan and delegates to the Detroit convention pledged to his candidacy.

During one of the television interviews in Detroit, Sen. Helms explained: "We have had an independent effort going on in North Carolina. The [federal election] law forbids me to consult with him and it's been an awkward situation. I've had to, sort of, talk indirectly with [Sen.] Paul Laxalt [the Reagan national campaign chairman] and hope that he would pass along, uh, and I think the messages have gotten through all right." Sen. Helms' candor may be refreshing, but the implications of what he says are truly disturbing for anyone who believes that independent expenditures were actually supposed to be independent from the campaign.

According to The Baltimore Sun, the National Conservative Political Action Committee, which is also raising funds to expend "independently" on behalf of Mr. Reagan and in opposition to President Carter, has revealed that its commercials for Mr. Reagan will "depend on the Reagan campaign strategy . . ." Some independence.

Now is the time for Mr. Reagan to call off this sleazy effort in his behalf.