About a year ago, when President Reagan's budget and tax programs were awaiting congressional action, John E. Swearingen, chairman of the board of the Standard Oil Co. of Indiana, wrote stockholders that management "wholeheartedly endorses the president's program (and) urges our stockholders to express their support for it."

"The package President Reagan has proposed," he said, "must be enacted, in its entirety, in order to . . . restore confidence in our economy and in our country."

When I wrote at the time about the Swearingen letter, and the barrage of business advertising and lobbying for the Reagan program, I noted that there was "a bit of a risk for business" in its embrace of a "supply-side . . . theory of uncertain validity."

"If its promise of abundance proves empty, and produces only higher unemployment, deficits and inflation," I observed, "then the adverse reaction could engulf not just Reagan and the Republicans but the business institutions which asserted that 'the future of our nation' requires that the program be enacted 'in its entirety.'"

Well, a year has passed, and Swearingen--unlike some other business executives--is sticking to his bet, at least rhetorically.

In his latest message to stockholders, Swearingen says that the "tax cuts of 1981 were too little and too late," but still predicts "beneficial results" when Reagan's full program for economic recovery is put in place. "Retrenchment and the recession currently under way are very unpalatable to many Americans," he concedes, "but the most effective medicine is frequently the bitterest. Even the bitterest aftertaste will fade as economic activity revives, new jobs are created and inflation is reduced."

Swearingen, like many other defenders of the Reagan program, argues that it is too soon to judge its effects, since it began only last October. He conveniently overlooks the fact that the accelerated depreciation provisions, which were the biggest of many boons to business, were retroactive to the start of 1981.

Nor does he dwell on the fact that his own company is stalling on the capital investment that the Reagan program was designed to stimulate. While Standard of Indiana increased its capital and exploration expenditures by $1 billion or 25 percent from 1980 to 1981, it is not budgeting a nickel's increase in the first full year of the Reagan era. A company spokesman says the freeze is taking place because of the recession and says it may be changed "when things turn around."

Swearingen falls in the middle of the business spectrum. He is not as much of a cheerleader as Richard L. Lesher, the president of the Chamber of Commerce of the United States. Lesher said earlier this month, when unemployment hit its postwar high, that "the economic news is getting better and it will continue to get better every week for at least the next two years."

But neither has Swearingen joined the leaders of the Business Roundtable, or the bankers, the realtors, the homebuilders, the savings and loan executives or even the officials at Mobil Oil, all of whom have called on the president for a "mid-course correction" to boost revenues, slow the defense buildup and reduce the deficit.

Swearingen is telling his stockholders to stick with the president, while delaying what a Standard spokesman says would normally have been about a 10 percent increase in capital spending.

Is that good enough?

The best answer may have come from Treasury Secretary Donald T. Regan in a speech last month called "Responsibility and Capitalism."

"The first responsibility of any capitalist is to himself," Regan told the audience at Philadelphia's Union League Club, "to make a good product and earn a fair profit."

"We have given you the tools," Regan continued. "Now we ask you to put them to work. We did not confuse Oct. 1, 1981, with the millennium. . . . At a time when inventories were high and plant utilization relatively low, it would have been unrealistic to anticipate an immediate surge of visible investment."

But Regan said "verbal assurances of long-range investment are not enough:" voters who watched business move with lightning speed to take advantage of the tax-credit-leasing provisions of the 1981 tax bill will measure that speed against the caution with which business is making long-term investment commitments.

The fact is that business bought in on the Reagan program in 1981 and business cannot bail out in 1982 without getting hurt. Either this program works, or the Swearingens and Leshers of this world are going to have some difficult letters and speeches to write.