NEW YORK — Owen Baser is at an age when most people are enjoying retirement.

Unlike most, at 75, Baser is just getting started in his career as an inventor. He's selling what he says is the first new type of door handle in more than 200 years — a design for those with physical difficulties.

That follows the trend among inventors in the past two years — a focus on safety-oriented, medical, computer technology and environmentally friendly innovations, according to Jeffrey Dollinger, chief development officer of the National Inventors Hall of Fame Foundation. Recent hall of fame inductees include Ethernet inventor Bob Metcalfe and Vint Cerf, one of the key architects of the Internet.

The high profiles of technology pioneers could be prodding more people than ever before to seek patents, as seen in the number of applications arriving at the U.S. Patent and Trademark Office. Last year, the office received 443,652 applications, spokeswoman Jennifer Rankin Byrne said, adding to a backlog that is expected to grow to 800,000 by the end of the year.

Baser, from Sacramento, Calif., was one of about 150 inventors at a recent USPTO conference, part of a wider outreach effort led by John Calvert, administrator of the patent office's Inventors Assistance Program and a former examiner. The office is educating inventors through clubs, universities and even high schools, to offer guidance on how to navigate the application process.

The complexity of applying for a patent is just one of the many obstacles inventors face. Baser's door handle and other ideas innovative enough to earn a patent can be the result of years, or even decades, of tinkering, testing and worrying.

Among the problems some of the inventors face: how to design a manufacturing process from scratch, how to enter a market to compete with a multibillion-dollar corporation or how best to get legal protection for their invention.

"A successful inventor — the ingenuity and knowledge base is almost secondary. The most common trait of an inventor is perseverance," said Dollinger. "They don't give up. They may not have hit big in the marketplace, but they expect to."

To their benefit, inventors tend to see these issues less as problems and more as puzzles. Most people look at everyday items such as laundry detergent, music earphones or even a house and accept them as they are. Inventors tend to be less accepting.

Mike Sykes, for instance, has spent the past 22 years inventing, refining and patenting a way to build homes in a more environmentally friendly way. His invention, the Enertia Building System, earned U.S. Patent No. 6933016 B1. The house uses the warmth of the sun and the coolness of the ground below the house to regulate the temperature inside.

"It's a house design that mimics that greenhouse effect that we see in the Earth's atmosphere," Sykes said. "The house makes its own weather."

No major homebuilders have yet shown interest in Enertia, but Sykes' goal is to usher the technology into mass production.

Sykes, 57, won the 2007 History Channel Modern Marvels Invent Now contest. An exhibit featuring the Modern Marvels finalists is on display at the U.S. patent office's headquarters in Alexandria, Va., through the end of June.

His invention reflects a spike in interest in innovations that will lessen the environmental footprint people leave, from the building of their homes to their personal consumption habits.

Sykes' 22-year odyssey may be longer than most, but other inventors were no less passionate about their ideas.

Kim Bertron, a 44-year-old pastry chef, become an inventor after one of her two daughters nearly died because a syringe broke as she was hurrying to prepare a diabetes drug for injection. Her solution? Invent a needle that would make it easier to quickly mix a diabetes drug and a diluting solution. She and her fellow inventors have heard from nurses who say the two-chamber syringe would be useful for other types of medication.