Retail sales fell 0.8 percent in May, but the figures for the previous month were revised upward sharply to show a 2.4 percent gain, the Commerce Department reported yesterday.

The large upward revision for April, primarily the result of a much higher estimate for automobile sales, means that the average level of sales for the two months -- $114.2 billion -- was 2.2 percent higher than the average for the first quarter of the year.

The May decline left sales 5.3 percent higher than they were in May 1984. The figures are adjusted for seasonal variations and differences in the number of selling days, but not for inflation.

Commerce Secretary Malcolm Baldrige said the figures indicate that "consumer demands are growing at a healthy pace." And he added, "Large increases in disposable incomes, boosted by tax refunds, should stimulate spending in June. . . . The expansion still has a green light."

Some other analysts, however, interpreted the retail sales data much less bullishly. Among other things, part of the higher consumer demand is being satisfied increasingly with goods produced abroad, adding to the nation's trade deficit, rather than to domestic production and payrolls, analysts said.

Sandra Shaber of Chase Econometrics said the erratic month-to-month change in sales is due in part to the delayed distribution of income-tax refunds. Overall, Shaber said, the sales numbers suggest "modest growth, much below the heyday of the recovery."

Robert Gough of Data Resources Inc., another economic consulting firm, declared, "The signals point to much slower consumer action over the summer and fall months."

Jack Carlson, chief economist for the National Association of Realtors, said the Commerce report confirms the sluggishness of the economy, especially a drop in auto sales in May, he said.

"The 3 percent decline in auto sales reflects the fact that consumers generally have come to the end of their spending spree and must work at reducing their debt burdens now," Carlson said.

The advance report on April retail sales showed only a 0.9 percent increase over the month before, with auto sales -- which account for about 20 percent of total sales -- falling 2.7 percent.

Those advance figures, as usual, were based on reports from only about 2,500 companies nationwide, the same sample on which the new May numbers are based.

With more complete information from a much larger 15,000-company sample, the April figure was revised upward.

There are often substantial changes between the "advance" and "preliminary" estimates of sales, with an average change between the two of about 0.5 percent, according to the Bureau of the Census, which collects the data.

April auto sales probably were boosted by special sales incentive programs, including low-interest-rate financing, offered on some models by car manufacturers.

There were disparate movements last month in sales levels among the various types of stores reporting, according to the Commerce report.

Durable goods sales fell 2.2 percent last month, with declines of 6.2 percent at building materials, hardware and garden-supply stores and mobile-home dealers.

Auto dealers' sales fell 3.2 percent after rising 6.5 percent the month before. Furniture, home furnishings and equipment stores reported a 4.8 percent rise in sales in May, following a 1.7 percent drop in April.

Sales of nondurable goods were unchanged in May after rising 1.3 percent in April.