Two weeks ago, in the second inning of a game against the New York Mets, Washington Nationals third baseman Vinny Castilla ripped a ball on a line toward the left-center field fence at RFK Stadium, took a couple of steps toward first base, and flipped his bat. A veteran of 15 major league seasons who has hit 309 home runs, he knows how to begin a home run trot.

"I crushed that ball," Castilla said. "There was no doubt."

The ball traveled toward the fence, near a sign advertising an airline. It hit the top of the wall, left of a mark that gave the distance from home plate: 380 feet. Suddenly, Castilla had to pick up his stride. It wasn't a home run. It was a double.

Afterward, Castilla was incredulous.

"That mark is wrong," he said. "It's 395 feet -- at least."

Close. This week, two Post reporters measured the distance to the wall in the left-center field power alley at RFK Stadium. Using a 300-foot tape measure and beginning at the tip of home plate, they measured out 300 feet, marked the spot, and continued to the wall, right at the spot marked 380. The conclusion: 394 feet.

Club officials asked the reporters to stop before other measurements could be taken, but the team agreed to bring in a surveyor who took measurements yesterday morning. The results confirmed what the players had suspected -- the marks in the areas midway between the foul poles and center field were incorrect. According to club officials, the actual distance -- measured with a laser -- to the mark that said "380" in left-center field was 394.74 feet; the actual distance to the "380" mark in right-center was 395 feet.

"It's been something that's been in people's minds," said Andy Dunn, the Nationals' vice president of ballpark operations. "The dimensions were on pads that make up the outfield fence, but the pads with the 380-feet marks were in the wrong locations."

Thus, prior to last night's game against the Houston Astros, club officials moved the "380" marks closer to the foul lines, so they represent, accurately, the distance from home plate. The club contends that the surveyor found measurements down the foul lines to be, essentially, accurate at 335 feet. The wall in center field, marked 410 feet, is actually 407.83 feet, Dunn said.

The debate about the fences has raged over the past few weeks in the Nationals' clubhouse, with players -- particularly Castilla and Jose Guillen, the right fielder -- openly suspicious that the fences were farther back than they were marked. Whatever the markings, the statistical evidence supports the theory that RFK Stadium vastly benefits pitchers over hitters.

"We thought that's how it would be," General Manager Jim Bowden said. "But we didn't know it would be like this."

In 46 games at RFK prior to last night, the Nationals and their opponents combined to hit 46 homers, an average of exactly one per game, the lowest in baseball. The next lowest is Kansas City's Kauffman Stadium, which averages one-third more homers per game; the highest rate is Cincinnati's Great American Ball Park, which serves up 3.13 homers per game.

Guillen has been vocal on the subject in recent weeks, and remained unconvinced by the surveyor's numbers.

"That's not right," Guillen said. "It's farther down the lines, and it's definitely farther in center field."

Though Guillen has said on several occasions that he would like to finish his career in Washington, he admits to being frustrated by his home park. The numbers show why: He has 18 homers on the road, one at RFK Stadium.

"I know myself," Guillen said. "I know my power. You guys know if I'm in a different stadium, I have 28, maybe 30 home runs."

Nationals President Tony Tavares has attended every home game, and has watched what Guillen and his teammates are seeing. In fact, Tavares and Bowden had a conversation during RFK's renovation over the winter, when the Nationals were preparing to move from Montreal.

"I told Jim I could tweak it, slightly, to be a pitcher's park or a hitter's park," Tavares said.

"And I told him," Bowden said, "that to bring the fences in with our team I didn't think made any sense, because I thought we're going to have to win with pitching and defense. We also had hitters who didn't have to hit home runs to produce runs."

Dunn said that he believes the mismarked distances -- in the "alleys," as the gaps between the center fielder and the left and right fielders are called -- were an "honest mistake."

"When I came to work here, I saw the dimensions, they told me what they were, and I didn't think, 'Well, I better go measure them to make sure,' " Dunn said yesterday. "You just trust that they're accurate.

"But then I started reading this stuff, and I wanted to make sure myself. I wanted someone on our staff to walk it off themselves."

So earlier this week, on the same day the Post reporters measured the field, Dunn walked off the distance himself, using a rolling measuring device. He didn't have confidence in the results, "so I got every measuring tape I could find." Finally, he decided to call Turner Construction, the contractor that installed the fences, to survey the distances again.

Tavares said he has marked six balls hit by Guillen that he believes would have been home runs in any other park.

"And if we're doing a contract with Jose, and I'm still here, I'll say, 'Jose, those count as home runs,' " Tavares said. "He can add them to his totals, and we'll negotiate from there. I know this isn't a hitter's ballpark."

Still, the topic has become one of the most prominent in the clubhouse. On Wednesday night, in a 3-2 loss to Colorado, the Nationals hit at least three balls that players felt would have been out of any other park, including one by new addition Preston Wilson, who came from Colorado, where homers traditionally come easily in the thin air. Wilson said yesterday that his ball, hit to center in the ninth inning, "wasn't hit with everything I've got. It is what it is."

But another player said, when Wilson arrived back at the dugout, he expressed his shock that the ball didn't travel out of the park.

"Those balls are gone," rookie outfielder Ryan Church said. "Any other place, they're gone. It's stupid. I'll just stick to hitting doubles."

Manager Frank Robinson, who hit three home runs at RFK Stadium as a Baltimore Oriole, is concerned that the mislabeled dimensions, and the park's size in general, could affect his team's mind-set.

"You have to know where you're playing," Robinson said. "We play here. We don't play in those other parks. Why would you say, 'That would have been a home run in Cincinnati?' We're not in Cincinnati."

Bowden is adamant that the park, whatever the measurements, has helped the Nationals more than it has hurt them. But he has watched his players become more and more frustrated, particularly as the team has struggled to win in recent weeks.

"I understand from a personal perspective, but we're talking about a thing called 'team,' " Bowden said. "Personally, of course we all want numbers. That's normal. I don't blame them. But we also want to win. And when you're winning, it's not as big an issue as when you're losing. When you're losing, and you're not getting numbers, it's frustrating."

Staff writer Thomas Boswell contributed to this report.

Nats outfielder Jose Guillen has hit 19 homers, but just 1 at RFK Stadium.

RFK Stadium's right field distance marker should read 335.77 feet. Other posted numbers in the outfield vary widely from recent measurements.