WASHINGTON (AP) _ One of the nation's most successful computer software designers cautioned Congress Wednesday against passing laws that would overprotect ''intellectual property'' by extending copyright protection to ideas.

''It's the nature of software for ideas to slosh and flow back and forth between competitors, companies and industries,'' Mitchell D. Kapor told a House subcommittee. ''If, as a software designer, I can use a program and learn from it without copying its internals, then I should be free to use the knowledge that I've gained as long as I expressed the ideas in my own way.''

The subcomittee is considering a revision of laws governing intellectual property - a phrase covering copyrights, patents and trade secrets - and heard from Kapor, software designer Daniel S. Bricklin and government officials concerned with copyrights and patents. Software refers to sets of instructions for computers, whether the instructions are stored on punched cards, magnetic tape, disks or chips.

Kapor designed a spreadsheet known as Lotus 1-2-3, which became a standard of the computer industry and made Lotus Development Corp, which he founded, one of the most successful software firms in the country. The firm is involved in a copyright suit against two competitors.

''There is no question, as I look at my industry, that there has been an unsteady but stubborn march to extend the scope of copyright,'' Kapor said. ''Twisting and straining each step of the way to secure additional copyright protections, too many companies seem to have decided that it's easier to sue their rivals than compete with them.

''Litigation is becoming a business tactic, not a practice of last resort. Software should not be an industry driven by litigation,'' said Kapor, adding that he was not complaining about the lawsuit.

Kapor said he sees no way to prevent potential competitors from profitiing from his company's efforts.

''If they can replicate our efforts or go them one better because our approach inspired them to do so, more power to them,'' he said. ''I would only call my lawyer if we found that these competitors had not just copied the idea, but the actual lines of code underlying it.''

James W. Curlin of the congressional Office of Technology Assessment presented the committee with an OTA study that said the United States' 70 percent share of the world's computer software market could shrink without better legal protection.

With continued innovation, the United States can keep outshining its foreign competitors, the study said, claiming that intellectual property protection encourages innovation by providing incentives for creation and security for investors.

Last year, software and related services were a $60 billion industry in the United States.