A key Senate Republican yesterday raised the possibility of spreading the administration's proposed 30 percent cut in personal income tax rates over four years instead of three to reduce the resulting federal budget deficits.

Sen. Pete V. Domenici (R.-N.M.), chairman of the Senate Donald T. Regan if there is any economic reason why such an approval would not work since it would provide the same predictability and consistency for taxpayers.

Replied Regan: "That's entirely possible, Senator, that the scenario would work."

Domenici and other committee members at a hearing, both Republican and Democrat, expressed concern that the economy would not perform as well as the administration predicts if its package and tax cuts is passed. With less economic growth, budget deficits would be higher, a point worrying the committee.

But while Regan did not reject the idea, he hardly endorsed it. "We don't think it would achieve as much for the economy as doing it over three years," he said. "It would not get the economy rolling as fast as if you do it 10-10-10."

The administration proposal, however, is not a string of three 10 percent cuts now. Rates would be reduced 10 percent on July 1, a further 5 percent Jan. 1, 10 percent more on Jan. 1, 1983, and finally 5 percent on Jan. 1, 1984.

Domenici is not committed to stretching out the tax cuts, but his committee staff is working out various ways in which that could be done. One possibility would be a 7 1/2 percent cut July 1, a further 3 3/4 percent on Jan. 1, additional 7 1/2 percent cuts for 1983 and 1984 and a final 3 3/4 percent for 1985.

From beginning to end, the administration cuts actually would take only 2 1/2 years to implement while an alternative such as the one above would 3 1/2 years. A number of economists have told Domenici that, in their opinion, changing the tax-cut timetable in such a way would make a little difference to the economy. On the other hand, the change could possibly reduce the size of any budget deficit.

Rep. Baber Conable of New York, ranking Republican on the House Ways and Means Committee, was skeptical about the virtue of offering alternative timetables at this point. "Republicans have got to the point of diminishing returns in arguing with themselves about the merits of multiyear tax cuts," he said.

Conable said stretching out the cuts is "a possibility," but he noted that most people who object to the administration program are objecting on the grounds that the tax cuts cover several years, not because of the size of the cuts.

Separately, Rep. Henry Reuss (D-Wis.) released the results of a study the Joint Economic Committee did of the administration proposals using the econometric model of Data Resources Inc. Such a model is a collection of mathematical equations describing relationships within the economy.

If the administration's proposals were adopted without change, and the Federal Reserve followed the monetary policy course the administratin wants, the results would be quite different from what President Reagan's economists have forecast, according to the JEC study. Economic growth is estimated to be slower, inflation and unemployment to remain higher and the budget in 1984 is estimated at $110 billion in the red instead of in balance as the administration predicts.

This is the sort of difference of opinion that concerns the Budget Committee, and they indicated yesterday no more readiness to accept the administration's predictions than those of other economists.

Meanwhile, at a Ways and Means Committee hearing, Harvard professor Dale Jorgenson told members that the president's business tax cut would, "to paraphrase Dave Stockman, create a coast-to-coast corporate soup line."

Jorgenson and a colleague, Alan Auerbach, backed their own less-generous proposal for a change in the depreciation allowances. The Jorgenson method would allow businesses to take all their investment write-offs in the first year, rather than spread out over several years.

The total to be written off would be determined by a formula aimed at calculating the life of the investment and the current value of now receiving write-offs that would otherwise only become available in later years. Although this idea, known as the First Capital Cost Recovery scheme, is backed by many experts, until recently it has been thought too big a change to win quick approval in Congress. Now a majority of Democrats on the Ways and Means Committee are leaning toward it, sources said.