They thought they had seen it all. But having to ask an agitated conservative, four-term congressman to leave the stage of RFK Stadium was a first -- even for the Grateful Dead.

Rep. John Kasich's enthusiasm at last Friday night's Washington concert was such that he tried to join the legendary rock band onstage -- only to be thwarted by organizers of the tour.

As the Ohio Republican was being urged off the stage, a witness reports, he was considerate enough to yell out his name several times, so those who didn't recognize him would know that he was a congressman.

When that didn't seem to sway the Grateful Dead's tour manager, who was trying to expedite Kasich's departure, the witness said the congressman suggested he could prevent the group from ever playing in this town again.

"Oh, come on," responded Kasich yesterday. "Telling the Grateful Dead you're a congressman is not going to get you onstage. This is way off the mark."

Kasich, who did have a pass, said he was led to believe that he would be allowed onto the stage, which was accessible by stairs. When he reached the top of the staircase, however, things didn't go smoothly.

"I said, 'Hey, why won't you let me on -- I can't understand why you're not letting me on,' " recalls Kasich. "I argued with him for a few minutes and then I left. I probably should not have argued with the guy. I don't think I was angry. I'm a pretty upbeat guy."

Others, none of whom would be named, tell a different story.

Kasich, 39, who looks more like an Eagle Scout than a Deadhead, has been variously described by those familiar with the scene as "obnoxious" and "disruptive."

Asked what "disruptive" meant in this context, a member of the rock band's entourage who witnessed the scene said: "I mean, he was potentially a threat to the show. The man wanted to be onstage with the group. We don't allow anyone we don't know onstage.

"Look, you have to understand, we can't have this kind of thing up there. We've got a group that needs to perform. We have equipment. We have lights. We have cables -- it can be dangerous. Someone can trip on a cable and knock out an amp."

Kasich had been initially invited onstage by Dwight Yoakam, the popular country singer who opened for the Grateful Dead. Performers frequently allow a few friends or supporters onstage during the show, all of whom are expected to wear passes and to behave. Also backstage last Friday night were Democratic congressmen Mike Kopetski of Oregon and Neil Abercrombie of Hawaii, who were guests of the Grateful Dead and not involved in the incident.

The Dead, whose concerts often generate mayhem and end with some arrests, are known to be particularly strict about who gets onstage. The fact that Kasich was onstage for Yoakam's show in no way guaranteed him access for the Grateful Dead's performance.

Consequently, when he attempted to get on the stage in the middle of the show, Cameron Sears, the Dead's tour manager, blocked him.

Kasich says that following Yoakam's show, he accompanied the country singer to his dressing room. It was only after an hour, says Kasich, that he asked Yoakam's people if he could go back onstage for the Dead. He says he was told he could.

But when Kasich got there, Sears told him that he needed to leave the area. At this point, say sources, Kasich began yelling at Sears. Kasich says if it appeared that he was yelling, it was only because the music was very loud.

After a tense few minutes, Kasich finally left the stage.

"Everyone backstage was talking about it," says one woman who was backstage but did not see the encounter.

Sears was apparently upset by the confrontation, and asked others backstage if they were familiar with Kasich.

"We knew he couldn't stop us from coming to Washington again -- but it was uncomfortable," said a source associated with the band. "This guy really had some problem -- it was really unfortunate."

Kasich, whose district includes part of Columbus, has a solid reputation on Capitol Hill as a bright comer who specializes in military, national security and budgetary issues. A member of the Armed Services Committee, Kasich is considered by Democrats to be thoughtful and flexible. In the last couple of years, he has formed an unlikely -- and shrewd -- alliance with liberal Rep. Ron Dellums (D-Calif.) to kill the costly B-2 bomber program.

As his spokesman said when told of the incident: "Doesn't sound like my boss."

Lesson 1: Don't Mess With Jim Rep. John Olver (D-Mass.), sent to Washington this week to fill the seat of the late Silvio Conte, had a first day in Congress that left even the most seasoned legislators breathless. No sooner was he sworn in Tuesday than the House launched into a frenetic display of back-to-back voting and complicated parliamentary maneuvering.

Leading the theatrics for the better part of four hours was Rep. James Traficant (D-Ohio), the often-recalcitrant gadfly who has made a career of ranting to the C-SPAN camera. Angry over losing an earlier battle, Traficant used his procedural rights to strike page after page of legislative language from a multi-billion-dollar appropriations bill.

Olver, not surprisingly, looked utterly lost.

At one point, he got up out of his seat and walked to where Traficant was railing to read over his shoulder.

Rep. Sam Gejdenson (D-Conn.), obviously realizing that his regional colleague had wandered into the TV picture and thus risked becoming identified early in his career with one of the House's most notorious rogues, quickly barked: "Sit down, John."

John promptly returned to his seat.

It's only just begun.