WASHINGTON – The heart of the Mets’ lineup made it perfectly clear yesterday it’s possible to hit the ball over the wall at RFK Stadium. Over and over again, to all parts of the park.

Carlos Beltran, David Wright, and Cliff Floyd homered in the first inning, and Carlos Delgado later tacked on a two-run shot, all off All-Star Livan Her nandez, starting the Mets on their way to a 13-4 win over the Nationals.

“We always felt that our lineup was great,” said Floyd, who hit his first homer of 2006. “You don’t have a relief point, from a pitching standpoint.You get into a little trouble, it becomes a problem for you real quick, and that’s what we try to do.”

Thanks in part to that strong offense, the Mets have won six straight games.

Washington, meanwhile, has lost five in a row, outscored 35-13 in that span. After Wednesday’s defeat, veteran Jose Vidro renewed a complaint heard often from the Nationals in the second half of 2005: RFK’s dimensions are too big, and that’s hurting the home team.

Nationals manager Frank Robinson said yesterday he hopes his players aren’t letting those sorts of thoughts affect them at the plate.

“If we’re going to start complaining about the size of this ballpark and whatever now,” Robinson said, “we might as well pack in and go home, because if we don’t, they’re going to be putting us in a little white jacket and carrying us out of here.”

For one thing, the Nationals’ lineup isn’t as stacked as the Mets’ is. New York’s 4-5-6 hitters – Delgado, Wright, and Floyd – went a combined 7-for-9 with six RBI against Hernandez.

“It seems like every other at-bat, we’re getting RBI opportunities, runners in scoring position,” Wright, who’s hit safely in every game this season and has 12 RBI, said. “You know, with the protection that we give each other throughout our lineup, you’re going to see some pitches to hit.”

The Mets went to work on Hernandez (1-2) right away. With two outs in the first, Beltran drove a 2-1 pitch to right. Outfielder Jose Guillen stood still with hands on hips, watching the ball’s flight.

After Delgado singled,Wright homered to left on a 3-0 pitch, and Hernandez hung his head. Floyd followed with a solo shot to right-center.

That’s how the game’s first seven minutes went: homers to right, left, and center, 4-0 Mets. It’s the first time Hernandez has allowed three homers in an inning during a decade in the majors, and when Delgado made it 6-0 with his third of the year, the burly pitcher had given up four deep balls in a game for the first time since April 7, 2001.

All told, he allowed eight runs – seven earned – on 11 hits in six innings.The Mets finished with 16 hits, adding five runs when they sent 10 men to the plate in the seventh against Joey Eischen.

Victor Zambrano (1-0) allowed three runs in five innings in his first start of the season.

“He was able to keep us in it,” manager Willie Randolph said.

That’s not much to ask these days against a Washington lineup in such a rut the team is trying to shake things up 10 games – and two wins – into the season. After the game, outfielder Brandon Watson and backup catcher Wiki Gonzalez were sent to the minors, and outfielder Ryan Church and infielder Brendan Harris were called up.