Football players are bigger, stronger and tougher that ever before, but advances in sports medicine have prevented an increase in serious injuries on the field, a new study finds.

The most controversial part of the study, reported in today's Journal of the American Medical Association, is its finding that injury rates did not differ significantly for players on artificial surfaces over the study period."We're doing a helluva job keeping injuries in a violent game from getting worse," said New York Jets' team physician Dr. James Nicholas, who led the study.

Nicholas and colleagues found the number of significant injuries - those requiring a player to miss at least two consecutive games - averaged less than one per game from 1960 to 1986.

The study also found the rate of "major" injuries - those requiring a player to miss at least eight consecutive games - was less than half that over the same period.

But the finding that injury rates did not differ on artifical surfaces drew howls of protest from the National Football League Players Association. The union said it contradicts an earlier study examining injury rates of high school players on grass and artificial turf fields,.

Players maintain the sure-footedness provided by artificial turf, and considered its most attractive element, also is its most damaging element. An attempt to change direction suddenly can put damaging stress on the knee because the joint pivots while the foot remains planted.

"That's why no one wants to play on turf. No one. Their careers are short enough as it is," said M.J. Duberstein, research director for the union.

The union, which contends the league will not make injury data available, did its own study during 1983-84 and concluded players sustained 20 percent more injuries on artificial surfaces. The data was gathered from injury lists released by the clubs and was published in most newspapers.

"Since it's been shown artificial turf is neither cheaper than grass, nor safer," said Duberstein, "you can go ahead and be cynical about why we get biased studies defending it ...

"The more injuries and the more severe they are, the more turnover you get," he said. "And more turnover means cheaper players."

But Nicholas countered, "I have no ax to grind. I'm not selling artificial turf."

Among its other findings:

- The knee was the the site of the greatest number of injuries, accounting for 39 percent of all significant injuries and 58 percent of major injuries between 1969-85, the study found.

- The position players most likely to suffer those injuries were runnings backs and cornerbacks.