What the tax rebels across the country apparently haven't stumbled onto yet is the fact that billions of dollars collected as taxes from ordinary citizens in recent years have never found their way into the public till. The culprits are the nation's giant untilities.

With the help of the "investment tax credit" and some fancy bookkeeping, dozens of electric and telephone untilities have managed to escape paying any federal taxes at all. They collect the taxes from their customers each month but are allowed to set aside a certain percentage of the take for untaxed investment capital to build new plants or improve existing facilities.

From 1962-when Congress passed the investment tax credit legislation to stimulate economic expansion-through 1976, privately owned utilities have beenallowed to write off an astonishing $4.3 billion in taxes, Which they collected from the citizen's pockets but didn't pass on to Uncle Sam.

The statutory tax rate on corporations range up to 48 percent. But in the past 20 years, thanks to the investment tax credit and other goodies, the utilities' tax rate skidded from 15 percent to little more than 1 percent. In other words, the utilities are paying federal taxes at a rate that is less than the rate for a family of four with an income of under $10,000a year.

The "phantom taxes" collected from consumers but never paid to the government are in effect interest-free, involuntary loans from utilities customers.

"The utilities have more tax write-offs than they can handle," griumbled on e congressional source. "They hide behind these tax benefits to boost earnings." Added another expert:"It's very simple. The utilities have made up an expense that doesn't exist."

Not surprisingly, the millions of dollars involved in this giveaway have become a problem for the state utilities regulators charged with setting the rates that power and telephone companies can charge. State regulatory commissions that want to pass along part of the savings generated by the investment tax credit are hamstrung by federal law, which doesn't require the utilities to share the benefits with its customers.

Cost figures compiled by the utilities routinely show projected expenses much higher than the real ones, based on the theoretical 48 percent corporation tax rate, which is almost never paid. More than one in four of the nation's biggest utilities had accumulated so many investment tax credits in 1975, for example, that they paid no federal tax at all.

Instead, the $84 million they collected as supposed taxes was written off as credits on their federal tax bill and became interest-free capital for the utility magnates to spend on often unneeded construction.

Spokesmen for the utilities nuderstandably defend these forced loans from their customers and insist the investment tax credit is necessary.

"it improves capital formation and productivity," an American Telephone and Telegraph Company official told us. If the investment credits were not available, he explained, the company would have severe "cash floe" problems.

Other utilities representatives claim the investment tax credit actually benefits consumers by helping to keep rates down and giving the companies interest-free capital to work with. Government experts, though, contend that none of the tax windfall ever finds its way back into the consumer's posket.

And it is obvious that the decision to build a new plant or to gussy up an existing one doesn't have to be weighted so carefulluif the involuntary "lenders" needn't be given justification for the investment.

The taxes paid by the utilities giants are so ridiculously low that some legislators, like Rep. Fortney (Pete) Stark (D-Calif.) have proposed exempting utilities from federal taxes altogether. The reasoning is that they already pay negligible federal taxes anyway, and exempting them entirely would at least put their true tax status out in the open. Utilities customers, therefore, would no longer be manking hidden, forced loans.

Footnote: An oversight subcommittee of the House Ways and Means Committee is planning to take a closer look at tax breaks for utilities.