If Roger Staubach announces his retirement as the Dallas Cowboys star quarterback Monday, one big reason may be that he's had six concussions within a year.

"Nobody's told him he can't play," said a Cowboy spokesman. He added that the repeated head injuries are a factor, but that Staubach's age (38) and wish to see more of his family are also important.

But in the last six weeks, according to the spokesman, Staubach went, on his own, to be tested by two different neurologists -- one in Dallas and one in New York. The quarterback has yet to disclose his reasons for seeking out the specialists (even though the team has paid for periodic neurological checkups following his past injuries) of the doctor's findings. But it is possible that Staubach has decided it's just too dangerous for him to keep playing.

Spokesmen for the Cowboys said they did not know the nurologists' names, and the team doctor, Dr. Pat Evans, refused comment until after Monday's press conference.

But according to sports medicine specialists at John Hopkins Medical School neurologists now have ways to monitor the effect of repeated concussions on an athelete's brain and to look for permanent damage.

A concussion is simply a knockout, a loss of consciousness that can last for a few seconds to minutes. According to neurosurgeon Dr. William Finey of Johns Hopkins, one of the head injury specialists for the Baltimore Colts, it can happen anytime to a football player gets hit so hard that his brain stem -- the top of the spinal cord -- collides with the ring of bone surrounding it at the point the brain stem leaves the skull.

That part of the brain stem contains the reticular activating system, the collection of cells that keep us awake. When those cells jar against the bone during a sudden deceleration, said Finney, "the lights go out."

The cells usually recover fast, and the victum wakes up within a minute or two. Staubach has had some concussions, including his most recent one in the last game he played for the Cowboys, that caused only dizziness or a momentary backout. But the one in December 1978, during a playoff game against Atlanta, knowcked him out for several minutes.

Neurologists disagree over whether concussions alone cause permanent brain damage. Dr. Joseph Martire, a sports medicine specialist and assistant professor of radiology at Johns Hopkins Medical School, said many schools bench a player who has two or three concussions in a single season, because of the theory that the knockouts slow down reflexes for weeks and make it harder for a player to protect himself from further injuries.

Finney believes the reflexes are slowed for only two or three days. But he said repeated concussions do produce disorganization of the brain waves, with abnormalities visible on a brain wave test. By the time football players finish college and prepare to enter pro football, Finney estimated that 20 percent of them have an abnormal brain wave pattern -- so many that he said such a test should be routine before a contract is signed.

But the real danger, according to Finney, is that if a player is hit hard enough to be knocked out, he may also suffer a contusion of the brain, which is much more dangerous.

A contusion is a bruising of the brain that actually can destroy brain cells. It happens when the cerebral cortex -- the layer of gray cells that make us think, feel and move -- is slammed against the inner surface of the skull that encases it. There can be small, slow hemmorrhages from the blood vessels overlying the cortex, which can put destructive pressure on the brain beneath them. Symptoms of the hemorrhages -- confusion, clumsiness or a subtle change in mental function -- may not show up for months, or may be aggravated by repeated injuries. But if an athlete suffers enough of the small hemorrahges, he gets "punchy."

Finney said that until recent years, neurologist had no test to diagnose a contusion or a small hemmorrhage overlying the cortex. But now, soon after an injury, they can look for a swollen area of the brain on a C.T. scan, a special cross-sectional brain X-ray.

They can also perform the scan months or years after injuries to look for lasting damage: the remains of hemorrhages, or an area of cortex that has been thinned and destroyed by pressure.

Finney said the neurologists who checked Staubach would have first done a complete examination, looking especially for sublte evidence of memory loss, a shortened attention span, trouble with word and number tests that tax the intellect or a lack of precision in performing fine movements. He said contusions are more likely to cause these problems than to produce muscle weakness or loss of sensitivity to touch.

Teams' heightened awarness of the danger of head injuries can be both a blessing and a curse to players. On one hand, they may help prevent what happened to John Huzvar, a Baltimore Colts player Finney remembers from the 1950s. He suffered so many brain contusions that he developed severe epilepsy.

On the other hand, concern about past head injuries can keep players who are healthy off the field. Martire mentioned one all-American linebacker who suffered a bad contusion two years ago, with a hemorrhage so large it had to be surgically removed. Now, Martire said, "his tests are completely normal (but) there isn't a team in the NFL that will touch him."

But the Cowboys don't feel that way about Staubach. "If concussions result in the way he plays, we ought to just hit everybody in the head with a hammer before the playoffs," one spokesman said.