The National Federation of the Blind yesterday filed a lawsuit against America Online Inc., contending that the Internet service provider discriminates against the blind because its system is incompatible with software that helps the visually impaired use computers.

The suit, filed in U.S. District Court in Boston, says AOL is violating the Americans With Disabilities Act by refusing to modify its programming despite several requests over the past year. Most aids that translate computer graphics and text into Braille or sounds do not work with AOL's current software.

"They say that 'we would really like to help you,' " said Curtis Chong, technology director for the federation. But, "in the end, they have not fixed the problem."

AOL spokesman Rich D'Amato said company programmers are working on a new version of its software, due out next year, that will be accessible to the visually impaired. "We are disappointed that they have filed their lawsuit," he said.

The screen-access scanners the blind use to "read" graphics depend on them to be tagged with words that describe the pictures. Many other Internet service providers, including MindSpring and AT&T Corp., use such labels, Chong said. But AOL's ubiquitous "You've got mail!" thumbnails, advertisements and other icons do not, making it difficult for the blind to maneuver through the system and find the information they want. The service provider's software also presents a problem because it requires customers to use a mouse click, instead of a keystroke, to perform some functions.

Chong said his office has fielded about 10 complaints a week for the past two years from blind consumers frustrated at not being able to hook up to AOL.

Cathy Schroeder, a computer programmer from Reston, attempted to sign up with AOL but was thwarted by pop-up boxes of advertisements. The boxes commanded her to click on them to continue. Schroeder, who is blind, remembers spending several minutes sweeping her mouse around and randomly clicking to try to get rid of them: "That's as far I got until I threw up my hands and said, 'I can't use this.' I couldn't even sign on."

Daniel Goldstein, a Baltimore lawyer representing the federation, said the suit is the first to demand that an Internet service accommodate blind users. He said the advocacy group singled out AOL because it is the world's dominant provider, with 19 million subscribers.

"It's so pervasive," he said, "that the blind feel particularly hurt by being shut out by AOL."