A presidential commission appointed by former president Carter in 1979 recommended yesterday that all employers be required to set up pension plans for their workers to supplement Social Security.

The commission, headed by Xerox Board Chairman C. Peter McColough, said that only about 48 percent of the people in private employment are covered by company pension systems, and because many such workers switch jobs they don't vest and thus end up with nothing except Social Security when they retire. It said only 28 percent of the retired private employes received company pensions in 1978.

The commission's report said that the best way to take care of retirement needs would be to mandate a "minimum universial pension system" (MUPS) that would force any public or private employer that doesn't already have a pension system in addition to Social Security to install one. This recommendation was the most controversial of a large number of commission proposals.

The employer would have to contribute an amount equal to 3 percent of payroll at a minimum to finance the minimum mandatory pensions. Many larger firms already having pension plans contribute two or three times that amount. The commission said the new plans should be open to any worker who is 25 and has at least one year of service with 1,000 hours of employment. It said vesting should be immediate (now it normally takes 10 years to vest) and that the benefits should be "portable," meaning that the worker could switch them to a new employer if he changed jobs or roll them over into an Individual Retirement Account (IRA).

The imposition of mandatory plans would affect mainly small businesses in the service and retail trades, which have the bulk of uncovered workers. To ease financing, the commission recommended a 46 percent tax credit on amounts put into the plans.

The U.S. Chamber of Commerce said iw was "quite alarmed" at the MUPS proposal, arguing that it would impose huge burdens on small firms regardless of ability to pay, reduce the discretionary income of low-income workers by draining off money available for wages and impose more regulation on business. It said the plan, combined with recommendations affecting Social Security, could end up costing $80 billion in the first three years. The National Association of Manufacturers also opposed the plan.

However, Rep. Claude Pepper (D-Fla.), chairman of the House Aging Committee, declared that the minimum universal pension scheme "doesn't go nearly far enough" in helping the aged. The American Association of Retired Persons called the plan "a good beginning."