Last month consumer confidence in the economy was lower than at any other time in the 15 years that American families have been surveyed.

Consumer confidence has been battered by a recession, high unemployment and soaring interest rates. Consumer expectations about the future are declining too, although the Conference Board, a nonprofit business research organization that conducts the surveys, said hopes for the future are higher than they were during either the 1974 or 1980 economic slowdowns.

The Conference Board said that 47 percent of U.S. households called current economic conditions "bad," up from less than 46 percent in February. In March 1981, only 31 percent of the 5,000 families surveyed called conditions bad.

"In rating present business conditions, pessimists now outnumber optimists by nearly 5 to 1," said a board spokesman.

Furthermore, the Conference Board said, consumers are scaling back their buying plans, after families raised their buying sights in February.

Until there is a recognizable upswing in consumer buying, one that will impel manufacturers to step up production, the nation will remain in a recession.

The research organization said that buying plans fell for "all of the major items covered: automobiles, homes, appliances and even carpeting." Only 7.5 percent of the families plan to buy cars, compared with 7.8 percent in February, while 2.9 percent plan to buy homes, down from 3.2 percent in February.

Fabian Linden, who heads the Conference Board's consumer research center, said that the marked reduction in the rate of inflation during the last year has helped check the decline in consumer expectations about the future.