The Patent and Trademark Office has decided to investigate whether it improperly granted a patent to a California man who claimed to have invented a common programming shortcut to fix the year 2000 computer glitch.

The unusual decision to "reexamine" the patent comes after the inventor, Bruce Dickens, asked Fortune 500 firms to pay him millions of dollars in licensing fees, regardless of whether they learned about the technique from him. Several businesses complained to the patent office that the method was widely known and used by programmers before Dickens said he developed it, and as a result does not deserve government protection.

The year 2000 problem stems from the fact that millions of computers were programmed to recognize only the last two digits of the year in a date, assuming that the first two would be 1 and 9. On Jan. 1, machines that have not been repaired will understand the year "00" not as 2000 but as 1900, potentially causing them to shut down or stop working properly.

Instead of painstakingly rewriting a program to represent all dates with four digits--with "1999" replacing "99"--the shortcut involves making the computer understand whether a two-digit year, such as "01," should be preceded by a "19" or a "20." A programmer chooses which years are in the 20th century and which are in the 21st by establishing a "window." A 30-year window, for instance, would have the program interpret the years "00" through "29" as 2000 to 2029, while years "30" through "99" still would have a 19 in front.

Dickens said he thought of the technique while driving to work in 1995. His employer, McDonnell Douglas Corp., applied for a patent in 1996. Concluding the invention was "new and non-obvious," the patent office granted the patent in September 1998.

But after Dickens sent bills to Fortune 500 firms this fall, a chorus of programmers and business groups charged that the technique is, in fact, blatantly obvious. Several computer specialists and trade associations have compiled lists of dozens of references to the windowing method in trade journals and computer standards manuals before 1995.

In a statement issued late Tuesday night, the patent office said its commissioner, Q. Todd Dickinson, ordered the reexamination of Patent 5,806,063 "after the discovery of information that was not considered when the patent was originally examined and granted."

The patent office noted that reexaminations ordered by the commissioner are rare.

Dickens's attorney, William Cray, expressed confidence in the validity of the patent. "Bruce has examined many of the articles that people have cited, and he doesn't see a problem," Cray said. "He still believes his invention was new and non-obvious."

Cray said a few firms already have agreed to pay Dickens, but he refused to specify how many. If every Fortune 500 corporation opted to shell out the fee, Dickens would wind up with between $165 million and $16.5 billion--depending on when the companies paid--for just the first year of the patent's 17-year life.

In the reexamination, the patent office will study literature and consult experts overlooked during the initial review process, patent experts said. Patent officials then will give Dickens an opportunity to respond.

Industry groups that called for the patent to be reexamined cheered the decision. "It affirms our initial belief that this patent never should have been issued," said Marc Pearl, a vice president at the Information Technology Association of America.

CAPTION: Bruce Dickens, shown here at his Laguna Beach, Calif., home, said he thought of his technique for fixing the Y2K glitch while driving to work in 1995.