Black and Decker Manufacturing Co., the nation's biggest power tool maker, has accused Sears, Roebuck and Co., the nation's biggest retailer, of patent and trademark infringement for allegedly copying one of Black and Decker's highly successful tools.

The tool is Black and Decker's Workmate, a portable sawhorse-vise combination that has been on the market about four years, and is now made in three models.

Sears' similar-looking device, advertised as a "Work Buddy" is not stocked in Washington area stores, but is listed in the latest Sears catalogs.

In U.S. District Court in Baltimore this week, Black and Decker sued Sears over the tool.

The lawsuit charges Sears not only infringed the patents on the product, but also Black and Decker's trade-marked name by giving the Sears tool a similar appelation.

In the petition, Black and Decker asks for unspecified damages for infringement and for the removal of the Sears product from the market.

Representatives of Sears and Black and Decker declined to discuss the details of the case.

The issue apparently is a touchy one because Black and Decker manufacturers some power tools which are sold under Sears' Brand names.

Whether the two companies discussed production of a Workmake for Sears, neither firm would say.

The Sears Work Buddy went on sale about three weeks ago and is displayed prominently in the company's new fall tool catalog.

Sears is generally acknowledged to be the biggest seller of power and hand tools in the nation. Black and Decker is the biggest power tool maker, with worldwide sales approaching $1 billion a year.

Patents on the Workmate are held by Inventec International Ltd., a British firm that licenses it to Black and Decker for world-wide sale and manufacturer.

Black and Decker began selling the tool in Britain in 1973 and has sold it in the United States since 1974.

The Workmate looks like a fancy metal sawhorse with a wood top rail. The top rail splits to form a long vise and clamp, designed to hold everything from a board to a bicycle.

Black and Decker's original Workmate, with adjustable legs for two working heights, has sold for from $59 to $89, a company spokesman said.

It was followed by two lower-priced versions, a single height model that sells in the $39 to $49 range and a new bench top version, that is being marketed at the National Hardware Show in Chicago next week. It will sell for $29 to $35.

Sears fall tool catalog lists that company's product at $67.88.