President Reagan's economic plan, designed to reduce inflation, has not lessened the belief of most Americans in the need for wage and price controls.

The weight of public opinion in the latest Gallup Poll is in support of controls, with 50 percent in favor of and 38 percent opposed to having the government take this action.

In the previous survey, conducted in early January, before President Reagan's inauguration, the results were virtually the same: 49 percent in favor and 40 percent opposed.

In contrast to the public as a whole, business and labor leaders have traditionally opposed controls. Labor leaders say wage controls unfairly penalize union workers, while business people want the opportunity to raise prices, and fear that controls will cause shortages in some commodities.

Proponents, however, point to the example of the Netherlands, Switzerland and West Germany, each of which has made great headway in controlling inflation and at the same time follows an incomes policy.

For almost 40 years the public has approved wage and price controls during wars or periods of severe inflation.

In 1966, opinion was evenly divided betwen those who favored and those who opposed wage-price curbs. But as inflationary pressures built during the latter half of the '60s, opinion began to shift in favor of controls.

In a survey shortly before President Nixon's 1971 imposition of a wage-price freeze, public support for controls had reached its highest point since the Korean War. Just after Nixon froze wages and prices, a Gallup Poll showed that Americans supported the move by a 5-to-1 ratio.

Furthermore, surveys conducted at regular intervals during the three phases of Nixon's economic program consistently showed that the public favored stricter as opposed to less strict controls.