Sears, Roebuck & Co. yesterday launched one of corporate America's biggest job cutbacks in recent years, announcing that it will slash about 21,000 office and receiving room positions at its stores across the United States.

Sears, by some measures the nation's biggest merchant, said in November that beginning this month it would dismiss or reassign thousands of the non-sales employees at its 863 U.S. stores to streamline operations. Until yesterday, however, there was no official word of how many thousands of jobs would be cut by the slumping company, only estimates that the total would fall below 20,000. The cuts are to be completed by midyear.

The 21,000 hourly and management jobs being eliminated consist of 3,500 full-time and 17,500 part-time positions, or nearly 7 percent of the company's retailing work force. Sears's big financial services subsidiaries, Allstate Insurance and the Dean Witter securities company, were not affected.

Gordon L. Jones, a spokesman at Sears's headquarters in Chicago, said the company did not know how many of the 21,000 job cuts would come through dismissals or how many of the affected workers could be transferred into sales jobs or positions that become available at new stores. Sears will have openings later this year in Burbank, Calif., for example, when it opens a new store there.

Sears officials, without giving specifics, said the cuts will help boost the company's sagging profits, which have been hit hard by the overall slowdown in U.S. retailing and Sears's own image problems.

In the third quarter -- despite earlier job cuts and cost-cutting efforts -- the company's profit fell 30 percent to $179.2 million on sales that rose 5.9 percent to $13.96 billion.

Analysts were skeptical. "It is certainly a step in the right direction, but it's not enough," said Kurt Barnard, publisher of the Retail Marketing Report.

Edward Weller, an analyst with Montgomery Securities, said the cutback was a tragedy for the workers involved, but long overdue for the company itself.

Barnard noted that Sears's operating costs, including payroll and administrative expenses, are believed to be the highest among major U.S. retailers. He also said Sears's key problem is that it has been unable to find a way to bring enough customers back to its stores.