For swimmers, runners and other athletes racing to set new world records this month at the Summer Olympics in Athens, every second counts.

But as competitors approach the limits of what is humanly possible, setting the fastest times may be decided not by seconds, but by milliseconds - - or less.

That has companies like San Jose's Symmetricom, a maker of precision timing devices, pondering the role that more sophisticated clocks could play in future sporting events.

"Times are coming in very close, and people will want a more precise timing source," said Bruce Bromage, a company executive vice president.

Bromage elaborated on this idea in a Symmetricom online newsletter, saying, "Every year, athletes push against the very limits of human potential. But as athletes begin to hit the ceiling of human ability, we'll no longer expect each year's performance to be better than the last."

Francois Peronnet, a professor at the University of Montreal and a leading expert on the progression of human athletes who was cited in Bromage's article, underscored this point by citing the record for the men's 100-meter dash.

The mark has fallen steadily since the beginning of the 20th century, from 10.2 seconds set by track legend Jesse Owens in 1936 to the current 9.78 set by U.S. sprinter Tim Montgomery in 2002.

Records have fallen due to better nutrition and health care, better training techniques and the fact that more people are taking part in competitions. Peronnet also cited the role of performance-enhancing drugs, which has led to a scandal involving some top U.S. athletes.

But he also noted, "You cannot run at the speed of light. ... We are slowly approaching the limit. Nobody knows exactly where the limit is. But the limit is probably not too far away. It would be difficult to improve the mark by a wide margin, because there is little margin for improvement."

That means world records could eventually become flat, he added.

Since the 1970s, speeds at most Olympic racing events have been recorded to the one-hundredth of a second, or two decimal places. One exception is the luge, a sport that involves incredible speeds recorded to the millisecond, or three decimal places.

Swatch of Switzerland, the official timekeeper at the Games, uses quartz- based clocks that can record to the millisecond, the company said.

Clocks use the vibration or motion within a material to set time. Most sporting events use quartz-based clocks.

But companies such as Symmetricom and Agilent Technologies make even more powerful clocks using Cesium atoms, which are known for being stable, making them even more reliable synchronization devices.

Atomic clocks have been used in a variety of research and military functions, such as keeping global positioning systems in synch.

Veteran Agilent scientist Leonard Cutler, who has done such extensive research on time and time-keeping that he is fondly referred to as Father Time at the Palo Alto firm, said atomic clocks are 10 million times more accurate than regular quartz-based devices. It's been used in experiments on physicist Albert Einstein's theory of relativity, he said.

But he didn't think atomic clocks would play a major role in recording time in Olympic competition, saying that keeping time to the nanosecond "would be way overkill."

Daniel Baumat, a vice president at Swiss Timing, a division of the Swatch Group that focuses on the Olympic Games, said by e-mail from Athens, "The assertion about the limits of human ability is not new. Look how many world records were broken this summer."

Baumat was optimistic about his company's ability to develop technology that can record time "to more than one one-thousandth of a second ... even as humans grow stronger and faster."

John Hirsekorn, Symmetricom's vice president of marketing, said as high- end time-keeping technologies, including atomic clocks, become cheaper, "their application in sports and many other areas will grow, and the ability for more precision timing in sports will be readily available."

Right now, Symmetricom's top-of-the-line clocks cost up to $45,000, Hirsekorn said. Among the company's biggest customers are Verizon Communications, the Department of Defense and the federal National Institute of Standards and Technology.

Peronnet said the Olympics and the entire sporting world will probably embrace more precision timing -- if only to maintain the thrill of competition.

"If we stick to the hundredths of a second, the marks will stall," he said. "There will be less excitement."