Gerald J. Mossinghoff was in China last week, helping engineer a minor diplomatic coup. A bit earlier it was Japan, for a round of international negotiations. And last night he was the guest on Larry King's nationwide night owl radio program.

Pretty heady stuff for a guy who heads an $80 million-a-year Commerce Department division full of people who wear rubber guards on their fingers to prevent paper-shuffling callouses.

Mossinghoff is the commissioner of patents and trademarks, reigning over an office that is normally so far out of the limelight that it is headquartered in Crystal City.

But the Patent and Trademark Office is a Very Important Place to thousands of businesses, and equal numbers of independent Gyro Gearlooses, who don't want anyone else producing their exclusive widget designs or selling soda pop under their registered trademarks.

Not only that, but the office is the apple of Commerce Secretary Malcolm Baldrige's eye, according to no less an authority than presidential counselor Edwin Meese III. Meese said so when he dropped by to offer President Reagan's personal congratulations at a recent ceremony honoring Mossinghoff's office as one of the best managed in all Washington.

So what does Mossinghoff, a lanky, genial lawyer who worked as a patent examiner more than two decades ago, think about his empire?

"We're a pretty good-sized paper factory," he said.

Yes, it is. There are more than 24 million documents on file in the patent side alone, so many that at any one time about 1.5 million of them are missing or misfiled. When a new patent application comes in, the patent examiners must search through the files by hand to see if a similar patent already exists.

The trademark side has more than 460,000 active "marks," each on paper and filed in towering stacks of "shoeboxes," metal versions of the real wooden shoeboxes the office used in the days of Thomas Jefferson, the nation's first patent examiner when he was secretary of state under George Washington.

What makes the office a center of attention these days is the administration's ambitious plan to replace the paper with electrons. The patent and trademark office is getting ready to enter the computer age.

The irony of storing a patent for the latest computer development in metal files on crumbling paper is not lost on Mossinghoff, who spent 15 years amid the space-age technology of NASA before taking over the patent office.

But that's not why Mossinghoff wants to modernize the process. The simple fact is that the cumbersome search-and-store methods mean that it sometimes takes four years to process a patent, sharply cutting into the 17 years of protection an inventor is supposed to get.

The administration figured that business deserved better than that. It also figured that business ought to pay for it. So last year, the government boosted the price of getting a patent or registering a trademark. A patent that cost $230 in 1980 now costs $3,200, although there's a half-price clause for small businesses and private inventors. Trademark registration prices increased from $35 to $175.

The money has been used to add more than 300 new examiners, and eventually will help pay the bills for buying computers and transcribing all that paper onto silicon chips.

By next year, Mossinghoff proudly reports, the office will process more patent applications than it receives--for the first time in eight years. In other words, it will stop falling behind in its work.

One of the first things Mossinghoff did was install a fleet of IBM word processors to take over the task of sending out an annual 80,000 or so patent opinions.

"We were still sending them out in longhand," he said. "In my view that was tacky."

Mossinghoff's "think-computer" zeal extends even to a staff newsletter, which he said he thought would be a good idea to help keep employes up to date on the automation plans. Employes walking through the lobby can punch up the latest office skinny on a computer display screen.

Mossinghoff is also involved in negotiations to coordinate automation with patent offices in Europe and Japan (hence his occasional globe-trotting), and recently traveled to China to meet with officials setting up a patent office there. That the Chinese have chosen the U.S. patent process, rather than the Soviet Union's, is considered an important step in furthering U.S-Chinese business relations.

Meanwhile, Mossinghoff is preparing for an annual event that honors the people who make his job possible: inventors.

The office will be having an open house this weekend to honor the American inventor of the year and induct five inventors into the national hall of fame.

It's only appropriate that this year's inductees include George R. Stibitz and Robert N. Noyse. Stibitz is the father of the binary computer. Noyse invented the silicon chip.