President Reagan has kept one campaign promise that has gone largely unheralded. He correctly suspected that the federal budget was loaded with waste, and he pledged to seek out and eliminate misspending.

He created a task force of business leaders and asked them to apply their managerial know-how and common sense to the problem. Its official title was the President's Private Sector Survey on Cost Control. But such a moniker couldn't last, and it quickly became known as the Grace Commission, after the drive and determination of its chairman, J. Peter Grace.

With a powerful push from the president, the commission has made extraordinary progress at cutting government waste against the stiff opposition of interest groups. For fiscal 1986 and 1987, this effort has saved close to $70 billion.

This amazing achievement has been documented out of government ledgers by the Office of Management and Budget.

Meanwhile, Congress is also turning to the Grace Commission's proposals for slashing government expenditures. One of every three members has joined Grace Caucuses, which have pledged to cut the waste out of the federal budget. The antiwaste drive is led in the Senate by Dennis DeConcini (D-Ariz.) and Gordon J. Humphrey (R-N.H.) and in the House by Buddy Roemer (D-La.) and Beau Boulter (R-Tex.).

Because of the Grace Commission's stunning success, it has been enlarged and revitalized as the United States Taxpayers Commission. The president met on July 7 with Grace, who set up the new commission, which will serve as the taxpayers' eyes and ears in Washington.

It will keep a permanent watch on how the taxpayers' money is spent. As Reagan later explained on his weekly radio broadcast: "J. Peter Grace and a group of dedicated business leaders are now forming the U.S. Taxpayers Commission to keep the focus on reducing costs rather than raising taxes. I expect they will bring renewed interest to streamlining federal operations and to assure that you, the American people, are getting all the government you are paying for."

The Taxpayers Commission is recruiting commissioners from the grass roots. It will seek a political balance of Democrats and Republicans, liberals and conservatives, who will seek new ways to fight waste, improve efficiency and cut spending. It will report back to the taxpayers on a regular basis on the misspending of government funds.

How to pay for yesterday's expenditures with tomorrow's revenues, meanwhile, is a troubling problem. For the spending rate is still too high and growing too fast. People cannot remain free and productive if a constantly increasing share of their earnings is taken by government and spent on its purposes rather than theirs.

Footnote: Jack Anderson has been co-chairman with Grace of the national effort to reduce waste in government. They will cochair the new U.S. Taxpayers Commission.