DAYTON, Ohio (AP) _ A proposed merger between AT&T and NCR Corp. comes at a time when NCR is at the zenith of its transformation from a maker of low-tech cash registers to a leading producer of innovative computer systems.

NCR Chairman Charles E. Exley Jr. said Monday his company opposes American Telephone & Telegraph Co.'s offer to buy NCR for $6 billion because it would distract NCR from its plans to market a new line of computers in the 1990s.

NCR was founded in 1884 when John Henry Patterson bought the National Manufacturing Co. and renamed it National Cash Register. The company nearly cornered the market in cash registers, creating thousands of jobs for the Dayton-area economy.

The company also developed a community-minded image. During a major flood in 1913, NCR workers turned out boats made from packing-crate lumber to rescue stranded citizens. And during the Depression of the 1930s, NCR set up a relief kitchen for stricken residents.

''If the independence of NCR is snuffed out, it will have some impact on the community,'' Exley said.

During World War II, NCR made motors for anti-aircraft rockets and other defense contracts. With materials scarce for civilian production, the company found a booming market in reconditioning old cash registers.

By 1960, the market for mechanical cash registers hit its peak, and the Dayton NCR complex boasted 33 buildings on 55 acres. But the company was hit with high costs and labor strife in the early 1970s, and the production of electro-mechanical cash registers ended in Dayton, with the loss of 16,000 jobs.

The company then stepped up production of electronic cash registers and started to lean more heavily on its line of business computers, which it began developing in the 1950s.

Last September, NCR announced it would replace its entire computer line with industry-standard machines that could communicate easily with each other. The company said it would produce the entire line - from tiny laptop models to powerful mainframes - using the same Intel Corp. microprocessors.

The move was the boldest yet by a traditional computer maker to contend with the industry's move to ''open'' systems, or those that follow industry standards so they easily can be connected.

Analysts said the new line of machines could strengthen NCR's position in the computer industry. The company is the nation's fifth-largest computer maker.

Exley said a merger with AT&T doesn't make any business sense for NCR.

''We think it would be a distraction from the great opportunity that we have for the product programs that have been announced over the last couple of months,'' he said.

And Exley said NCR employees are concerned about the offer.

''It brings an entirely new element into the scene that our people haven't confronted before,'' he said.

NCR employs 56,000 workers at its 1,200 offices around the world, including about 5,400 at its Dayton headquarters.