After a career of hard hits and glory, the most difficult issue many NFL players face is knowing when it is time to walk away from the only job they have known.

Dozens of players are grappling with the question in the waning weeks of 1999, a season that has included the decline of established NFL stars and the emergence of young upstarts.

In San Francisco, quarterback Steve Young insists he'll return for a 16th season despite concussions that have sidelined him most of the year. In Miami, Dan Marino is under fire about his arm strength and ability after a painful Thanksgiving day performance in which he threw five interceptions in a 20-0 loss at Dallas.

And in Washington, some wonder if the clock isn't ticking on cornerback Darrell Green and running back Brian Mitchell, the Redskins' most respected veterans, who have shaped the team's identity and consistently given fans their money's worth.

There are no indications either is contemplating retirement.

At 39, Green can still hold his own when compared to most of the starters at his position, arguably the toughest in the game. And Mitchell, 31, exploded with a 45-yard kickoff return Sunday against Philadelphia that nearly spared overtime, answering critics who say he has lost a step.

Only a lucky few in the NFL make the decision about when to retire. Most often it is forced by injury; the arrival of a younger player who is incrementally faster, tougher or stronger; or, increasingly, the squeeze of the NFL salary cap, which forces every player to justify his spot on the roster through weekly production on the field.

Three former Redskins made the decision to retire on their own: Hall of Famers Sonny Jurgensen and Bobby Mitchell, who walked away after pro careers of 18 and 11 years, respectively, and linebacker Ken Harvey, who stunned teammates in August by retiring on the eve of his 12th season midway through training camp. They know firsthand the wrenching issues in store for veteran players.

In 40 years in the game, Bobby Mitchell, now the Redskins' assistant general manager, never came across a player who wanted to retire. Nor did Jurgensen, a color commentator for Redskins radio broadcasts.

"It's a game you've played all your life. It's something you've done since you were a little boy," Jurgensen said. "You don't want to give it up."

Statistics may attest to a decline, and fans and media may harp. But according to Jurgensen, athletes are the first to know when it's time.

"When you've played at a high level, you just don't want to play out the string when you're not capable of playing at the level that you used to play," Jurgensen said. "And that helps you in your decision-making. The awareness of that and dealing with that is difficult. As much as you like to play, you feel it: You can't throw it, you can't run, you can't get open."

That doesn't mean aging players aren't defiant.

"Back in my day, you'd have to rip the jersey off the guy," Bobby Mitchell said. "[They'd say,] 'Go home! You can't play anymore!' And they'd be crying, screaming, 'I know I can play!' "

The passion to keep going is based partly on love of the game, Jurgensen said, and partly on the fear that life afterward will offer nothing comparable.

Jurgensen was among the more successful at cheating time.

After elbow surgery in 1967, Jurgensen's surgeon told him it was time to find something else to do--his throwing arm would never be the same. The quarterback convinced the doctor to keep the opinion to himself, explaining, "I want to fool them as long as I can." He played another seven seasons, and threw five touchdown passes in his first game back.

When he retired in 1974, it was because he balked at the role coach George Allen was offering. With Billy Kilmer and the young Joe Theismann on board, Allen told Jurgensen he was "a luxury" the team could no longer afford.

"Billy wanted to be traded at that time; they wanted to play Joe," Jurgensen recalled. "Therefore, I wasn't in the mix. But if Billy had forced a trade, he said then we want you back. I said, 'Well, I don't understand that. . . . ' You don't want to end up that way. You want to contribute."

Harvey's thinking was similar last summer.

He had worked hard to recover from the knee surgery that cut short his 1998 season. Playing with pain was nothing new. But his body wasn't reacting as it had in the past. One leg was weaker than the other. Once-automatic reactions were slow in coming. His mind could make plays that his body could not.

Harvey prayed about it. He also consulted close friends and former players Tim Johnson and Monte Coleman. Then he decided.

"I didn't want to be a non-contributing factor on the team," he said. "I just didn't want to be somebody who was hanging on."

Bobby Mitchell stunned his teammates 21 years earlier by retiring on the eve of his 12th NFL season after training camp. When he was drafted in 1958, Mitchell planned to play five or six years. But a decade later, he had never been injured, never had an operation and was running just as fast and setting as many records as before.

"Then, mentally I started worrying about getting hurt," Mitchell said. "I felt I was overdue in my mind. So the slightest thing that would happen to me, I would panic, thinking, 'Aw, man! I guess this is when it's going to happen!' Well, you can't play football like that."

When he tore a hamstring, his decision was made. "I called it off right there," Mitchell said. "I didn't want to limp up and down the sideline."

Free agency has altered players' thinking about retirement, Mitchell said. With more movement among NFL teams, the bonds between player and coach, player and management have frayed. Coaches can no longer stockpile loyal warriors, and players are under no illusion otherwise.

But as free agency forces veterans out one door, it opens doors elsewhere, as the Redskins' current roster attests. Left tackle Andy Heck, 32, found new life with Washington after being released by Chicago. So did wide receiver Irving Fryar, 37, who retired after his stock dropped in Philadelphia.

"Everybody has a different opinion of someone's skill level," Jurgensen said. "That's why older guys have an opportunity to go to another team because of free agency to play another couple years."

But it is impossible to picture Darrell Green or Brian Mitchell in any uniform other than a Redskins jersey.

Said Bobby Mitchell, who has known both their entire pro careers: "I can't speak for them. But I don't picture Darrell or Brian concerned about what the public thinks they can do at this point. They have been put on the hot seat so many times over the last years that they feel that there is a dependability issue out there. You always want to walk away knowing you gave what was expected of you, right up to the last minute. It is hard to do that, no matter how good you are."