Retail sales blossomed along with the spring flowers in May, but analysts warned that the improvement in business was due as much to spring weather as to any resurgence in consumer spending.

Sears, Roebuck & Co., the nation's biggest retailer, reported its strongest sales gain since last September, F. W. Woolworth Co. had its best month since April 1981, and both J. C. Penney and Montgomery Ward posted sales increases in May after suffering sales declines during the first four months of the year.

"What we've seen is a bounce-back after the weather-affected April," said analyst Jeffrey Edelman, who researches retailing companies for Dean Witter Reynolds Inc.

At Hechinger Co.'s annual stockholders meeting yesterday, Chairman Richard England said a spring surge in sales was responsible for the increased first-quarter revenues for the Washington do-it-yourself chain.

Sales ran behind last year during "11 continuous weeks of bad weather," but in the last two weeks of the quarter produced "a complete turnaround," England said. "In two weeks we made up the deficit and were able to report a 5.5 percent increase in sales."

The same spring sales surge benefited most of the big chain stores that released their May sales data yesterday. But no analysts were predicting the upturn would continue. Instead, they said no significant improvement in store traffic will occur before July, when taxes are to be cut and Social Security benefits boosted.

The retail recovery may not occur before fall, warned analyst Jeffrey Feiner of Merrill Lynch, Pierce, Fenner & Smith Inc. "Retailing is going to be Dullsville for the next few months," he predicted. "The consumer doesn't have a need to come back to the stores until the back-to-school season."

Chicago-based Sears, the nation's largest retailer, said sales for the four weeks ended May 29 were $1.55 billion compared with $1.44 billion for the period a year before. For the year so far, Sears sales were up 3 percent to $5.97 billion from $5.79 billion a year ago.

The May results were the best for Sears since a 9.3 percent sales gain in September 1981 and were by far the strongest of the year. In April Sears showed only a 0.002 percent sales increase after gains of 2.1 percent in March and 2 1/2 percent in February when the retailing fiscal year began.

Sears Chairman Edward R. Telling said sales for the month that included Mother's Day were particu- larly strong on air conditioners, microwave ovens, video games, paint and tires.

Sales of most big-ticket items generally were lower in May, however, apparently reflecting the spread of the recession into upper-income brackets. Monroe Greenstein, an analyst for Bear, Stearns Inc., said sales of designer apparel, in particular, were beginning to be eroded.

"The effects of the recession so far this year has been much more pervasive," Greenstein said. "Last year it was confined to lower- and middle-income consumers."

Penney, the third-largest retailer, based in New York, said May sales increased to $833 million from $802 million in the 1981 month. For the first four months of the fiscal year, sales decreased 1.1 percent to $3.28 billion from $3.31 billion. Walter J. Neppl, Penney chairman, said the May sales gain reflected increased buying of apparel and such seasonal merchandise as patio furniture and barbecue grills.

No. 6 Ward, which is owned by Mobil Corp. and is based in Chicago, said May sales increased to $435.3 million from $413.2 million, but poor showings the previous months still kept sales down 5.7 percent for the first 17 weeks of the fiscal year from the year-ago period. Sales for the year to date were $1.6 billion compared with $1.7 billion.

No. 2 K mart Corp. of Troy, Mich., said May sales were up 7.6 percent to $1.3 billion from $1.2 billion. For the 17 weeks ended May 26, K mart said sales rose 7.9 percent to $4.9 billion from $4.6 billion.

No. 8, May Department Stores Co. of St. Louis, which owns the Hecht Co. of Washington and Baltimore, said sales rose 9.3 percent to $273.5 million from $250.2 million. Year-to-date sales rose 5.2 percent to $1.01 billion from $958.4 million. May is based in St. Louis.