Consumers' reluctance to spend more in a recession provided the nation's major retailers with sluggish sales again in September, and industry analysts warned that sales might show little improvement until the Christmas season begins.

Two of the top five retailers reported sales declines, while the other three -- including industry leader Sears, Roebuck & Co. -- said sales rose less than 3 percent.

Walter Loeb, a Morgan Stanley vice president and retail analyst, called the sales figures "weak, as expected. Consumers are being extremely conservative and still impacted by recession."

"The consumer has the ability to spend more if the consumer wants to," said Monroe H. Greenstein of the investment firm Bear, Stearns & Co. "But the retailing consumer is very cautious and is afraid to spend money, primarily because their neighbor is unemployed."

September sales "were pressured by a combination of sluggish economic activity, high unemployment levels and continued poor levels of consumer confidence," said Jeffrey Feiner, an analyst at Merrill Lynch Pierce Fenner & Smith Inc.

Retail sales have been poor since June as consumers, worried about the recession and their jobs, cut back on purchases and paid off bills instead.

Yet many economists say the economy's recovery will have to be ignited by higher consumer spending. A boost in sales would trigger new orders by stores that, in turn, would allow manufacturers to increase production and perhaps hire back laid-off workers.

The Reagan administration had expected consumer spending to pick up after the July 1 cut in income tax rates and recent declines in interest rates.

Those factors still might help raise spending, but perhaps not until the Christmas buying season begins after Thanksgiving, analysts said.

Chicago-based Sears, the nation's largest general merchandiser, said domestic sales for the five weeks ended Oct. 2 rose 2.2 percent to $1.9 billion from $1.8 billion a year earlier. Sales in the 35 weeks to that date were up only 1.7 percent.

K mart Corp., the No. 2 retailer, said its September sales fell to $1.5 billion from $1.6 billion. K mart executives said sales for the 35 weeks ended Sept. 29 were up 2.8 percent from the same period of 1981 to $10.4 billion.

Third-ranked J.C. Penney Co. said sales climbed 2.6 percent in September to $952 million from $928 million.

F.W. Woolworth Co., the fourth-ranked merchandiser, said September sales were up 3.5 percent in the United States. The figure included sales at the company's U.S. Woolco discount stores, which it is planning to close at the end of the year because of poor performance.

No. 5 Montgomery Ward, the struggling unit of Mobil Corp., said sales fell 5.5 percent to $477 million from $505 million. Sales for the 35 weeks are off 4.7 percent from a year ago to $3.4 billion.

Sales of May Department Stores Co. of St. Louis -- parent of Hecht's -- were up 6 percent.