Sears, Roebuck & Co. has told 20,000 managers their salaries will be frozen for at least a year, but analysts believe the pay freeze is just the tip of a cost-cutting iceberg for the nation's No. 1 retailer.

Analysts said they expect Sears to announce major cost-cutting moves after the first of the year - aimed at paring expenses by $500 million to $1 billion.But a Sears spokesman, asked about further cost-cutting plans, said: "At this point I'm not aware of any announcement . . . or any such plans in the pipeline."

Last week, Sears informed 20,000 salaried workers their 1991 salaries would be frozen at present levels. Those workers normally would have expected pay raises of 5 percent to 7 percent.

"The salary freeze is part of the company's ongoing, company-wide cost-reduction program," the Sears spokesman said Thursday.

"It involved all levels of Sears management, in its corporate offices and in the domestic merchandise group," he said. "The policy is effective beginning Jan. 1 for 12 months and would be reviewed as conditions warrant after that 12-month period."

But securities analysts said the pay freeze is just the beginning.

"I still think there's probably a bigger announcement coming, probably early next year, which will entail a much bigger cost-cutting program," said Daniel Barry, a retail industry analyst at Kidder, Peabody & Co. in New York.

Analysts said elimination of furniture departments and the shutdown of unprofitable or marginal stores are among the possibilities open to Sears.