SAN FRANCISCO – Cisco Systems sued Apple Inc. in federal court yesterday, saying the computer maker’s new iPhone violates its trademark.

The lawsuit, filed in U.S. District Court for the Northern District of California, came just a day after Apple CEO Steve Jobs unveiled the Apple iPhone in dramatic fashion at a trade show in San Francisco.

But even while Jobs was trumpeting the product during his keynote address to Apple faithful, the matter of the product’s naming had not been resolved behind the scenes between two of the biggest names in Silicon Valley.

San Jose-based Cisco, the world’s largest network-equipment maker, has owned the trademark on the name “iPhone” since 2000, when it acquired InfoGear Technology Corp., which originally registered the name.

And three weeks ago, Cisco’s Linksys division put the trademark to use, releasing an Internet phone called “iPhone” that uses the increasingly popular Voice over Internet Protocol, or VoIP.

But on Tuesday, Jobs unveiled Apple’s own iPhone, a “game-changing” touch-screen-controlled cell phone device that plays music, surfs the Web and delivers voicemail and e-mail.

Apple spokeswoman Natalie Kerris said she could not immediately comment on the lawsuit.

Cisco said Tuesday it had been negotiating for several years with Apple over a licensing agreement, but that Apple lawyers had not signed and returned the final contract.

Cisco is seeking injunctive relief to prevent Apple from copying Cisco’s iPhone trademark.