Research In Motion Ltd., a Canadian company that makes BlackBerry devices, has been locked in a court battle for more than four years with privately held NTP Inc., which contends that RIM unfairly used some of its patents.

The two companies reached a tentative settlement of $450 million early last year, but the deal fell through. Some analysts have estimated that a settlement at this point could cost RIM as much as $1 billion.

U.S. District Judge James Spencer will hear arguments beginning at 9 a.m. EST (1400 GMT) from NTP, which wants the judge to halt U.S. sales and shut down U.S. BlackBerry service. The judge granted such an injunction in 2003 but stayed it pending RIM’s appeal.

RIM has denied any patent infringement and contends that a court order halting U.S. service would be premature. It said in court documents there is an “exceptional public interest” in maintaining uninterrupted BlackBerry service, especially for workers in national security, health and safety.

The small devices to send and receive e-mail — which can also have organizer, cell phone and other functions — are used by about 3 million Americans, including Bush administration officials, members of Congress and executives. Some users have complained about thumb injuries from overusing the tiny keyboards on their so-called “CrackBerries” to send a steady stream of messages during meetings and while traveling.

NTP has suggested giving U.S. BlackBerry users a 30-day grace period if the judge decides to issue the injunction.

“Win, lose or draw, this is (a case in which) fast justice is better than slow justice,” said Don Stout, co-founder of NTP, a small Virginia patent-holding company.

A top RIM executive said the company has developed and tested a technical workaround to allow BlackBerry service to continue even if RIM loses the patent fight.

“We’ve got dozens of customers using it and we haven’t had one complaint,” RIM co-Chief Executive Jim Balsillie told a technology conference in Canada on Thursday.

Among the alternatives to the BlackBerry is the Treo 650 smartphone made by computer and smartphone maker Palm Inc. Both devices offer phone and e-mail service, access to personal calendars and the Internet.

RIM is expected to urge the court to give more time to the U.S. Patent and Trademark Office, which is reexamining the NTP patents. Earlier this week, the patent office issued an administrative decision rejecting one of the patents at issue.

Spencer also will hear arguments from U.S. Justice Department lawyers, who want reassurance that government BlackBerry users will be carved out of any shutdown.