Pressure gauge: to measure Nationals slugger Jose Guillen's ability to keep a lid on his temper, watch how he handles the heat of the N.L. East pennant race

Everybody is a seismologist when it comes to Jose Guillen.

They interpret the visible signs--the minitremors that rise forth occasionally they, throw buildup of pressure beneath the surface--and they predict, with all confidence, that it is only a matter of time before Guillen explodes like a full-blown volcano.

True enough, there have been signs, subtle though they may have been, pointing that way for Guillen, the Nationals' volatile right fielder and offensive engine.

There was the miniblowup in the dugout when one of his pitchers failed to retaliate for a beanball at Guillen. There was the thinly veiled slam in the newspaper at some unnamed teammates whom Guillen felt were unwilling to play through pain. There was the near brawl in Anaheim when Guillen had to be restrained from going after his ex-teammates.

As of yet, however, there has been no eruption.

Largely because of Guillen's potent bat and his thirst for playing every day no matter how painful his injuries, the Nationals are staying in the race for a postseason berth. Although Washington squandered the 5 1/2-game lead it held in early July, it remains an improbable contender with two months remaining in the season.

In contrast to his checkered past, Guillen at his best has been a model teammate in Washington. When Livan Hernandez began shouting angrily to reporters one day last week, it was Guillen who put his arm around the pitcher and calmed him down until the anger had passed and Hernandez was able to speak in quieter tones.

All season long, Guillen has played through pain--in his shoulder (which required a cortisone shot just after the All-Star break), in his ankle and, lately, in his wrist. The pain in the wrist, caused by another inside fastball. was so bad that team officials expected Guillen to miss the entire series against the Braves last week. Instead, he was in the lineup all the games.

Entering the week, Guillen led the Nationals in games played (99), hits (115), homers (19, 18 of which have come on the road) and RBIs (58). As long as the club keeps Guillen from blowing up, it believes it stands a chance to play in the postseason. But everyone knows an eruption could come at any time.

"But I don't try to put out his fire," says Nationals manager Frank Robinson. "Why take that away from him? That's who he is. That's what makes him the great player that he is."

As he leads the Nationals toward what he hopes will be a playoff spot, Guillen has undertaken a simultaneous mission to clear his name and clean up his reputation. Throughout baseball, he is viewed as a problem child, a bad guy, trouble in the clubhouse. That reputation was sealed, perhaps permanently, last season in Anaheim. In September, just as the pennant race was heating up, Guillen was suspended by the team after a confrontation with manager Mike Scioscia.

"It hurts me so much," Guillen says. "You know why? Because people have no idea what happened last year. They don't know the real truth. When I go home (to the Dominican Republic), sometimes I cry a lot because people on the street, they think I'm an ass. Like, they think I'm the worst guy in baseball. And they don't know the truth."

Here's the truth about Guillen: His passion for playing and for winning runs so deep and so hot that sometimes he no longer can keep it all inside, and like lava in a volcano, the passion rises to the surface and spills all over the place. Almost all of Guillen's "incidents" during his career were caused by his being too competitive. Even the Scioscia incident began when Guillen was removed for a pinch runner late in a critical game.

"I just want people to know one thing about Jose Guillen," Guillen says. "All he wants is to play every day and win."

After the benches-clearing staredown between the Nationals and Angels in Anaheim--the one in which Guillen had to be restrained from going after the Angels--Guillen called Scioscia a "piece of garbage." That prompted Angels reliever Brendan Donnelly to say, as tactfully as possible: "There's a reason why he's been with so many teams and why it's gone bad for him each time." Scioscia wouldn't comment when he was asked last week about Guillen.

The Nationals are Guillen's eighth big-league organization since the start of the 1999 season. Last April, Washington picked up its 2006 option on Guillen's contract.

"Every time he goes to a new team, in the beginning you hear about what a great guy he is and a great teammate he is," an executive in the American League says. "But then something always happens. At a certain point, that's a real track record, in the same way that somebody's career numbers are a track record."

The Angels must have been nodding and smiling smugly when they heard about Guillen's outburst in the dugout on July 8. After getting hit by a pitch from Pedro Martinez and teammate Esteban Loaiza failed to retaliate, Guillen got into a shouting argument with Loaiza and catcher Brian Schneider in the dugout. A similar incident in Anaheim last season was the start of Guillen's troubles with the Angels.