"Remember, this is the 1960s," comedian and emcee Robert Klein reminded the 11,000 youths and adults jammed between the reflecting pool and the Lincoln Memorial yesterday to help film part of the rock musical "Hair."

"Think sixties," said Klein.

For some that was not hard at all. The sights and sounds were echoes of the events and turbulence that shook and in some ways formed their lives during the 1960s. For others it was a glimpse back to a period that, while it had not touched them, is nevertheless a central part of a generation's folklore.

Pam Kramer, one of the thousands who came to the Mall yesterday, said she was there because she was curious.

"I wanted to see if it would be real people from the '60s or kids dressed up. It's mostly kids dressed up," Kramer said. "I'm 22, and I was right in the middle. I'm too old to feel comfortable with the people here today and too young to remember this."

Sue Brown, a 25-year-old Arlington resident, said she wasn't too young to remember it. The day was one for "bringing back memories," she said. She brought along her son Chris, 4, but admitted, "He'd rather go fishing. But when I first read about this in the newspapers, I said immediately, 'I'm coming.'"

The musical, antiestablishment in tone and tribal love in mode, became a symbol of the '60s, and the producers of the movie decided to film three major musical numbers from the show near the Lincoln Memorial.

So they had let it be known through news paper articles, ads in student newspapers, and in television and radio announcements that "young student types" were invited to participate by acting as background.

The scene, the press release said, "will be a huge 1968-style Be-In." Students were advised that those who will be featured in the film, to be released next winter, will be those wearing "appropriate garb, that is, the costume of a flower child" or blue jeans and work clothes.

So yesterday they came, with frizzed hair and Frisbees draped in ponchos, wearing blue jeans and boots. There were flowers everywhere - daisies in their hair, daffodils in their buttonholes, and tulips in their hands and headbands. They carried signs "Stop the War." "Make Luv, not War," and even yelled "Tricky Dick" at a man who wore a Nixon mask and obligingly posed for the hundreds of pictures.

But it wasn't the '60s, it was a nice spring day and one could be there without believing in any particular cause or conflict.In parts of Washington there were other demonstrations yesterday, including one to make Elvis Presley's birthday a national holiday.

"Everyone is in range for the camera," Klein assured the mall crowd at one point. Everyone, he said, "will get your puss in the movie that will be seen by four trillion people all over the world."

Yesterday's flower children had various reasons for wanting to participate.

"Why not?" responded Victoria Hirschland, 19, a George Washington University student, when asked why she had come. "It's Saturday, and there's no school. I was part of this. My mother was one of the original hippies. I went to Woodstock. I called my mother and she gave me hints on what to wear. She told me to wear as little as possible." Consequently, Hirschland was wearing a skimpy top, a skirt, and her grandmother's black velvet opera coat, her hair frizzed for the occasion, dandelions in her hand.

"I thought today would be a big party," said Mark (Engus) Englehart, a 19-year-old George Washington student, who wore a multicolored Afro wig and no shirt. "I was too young for the demonstrations. There was so much energy and activism then. I guess I kind of missed that.But there also was so much conflict then. It really was like a nation divided."

The youths were lured not only by the chance to appear in a movie, but also by entertainers who performed, including the Rosslyn Mountain Boys, Catfish Hodge, Bonnie Raitt. They heard Melba Moore and Ronnie Dyson sing, and watched the Twyla Tharp dancers stage a ballet - and saw someof the staging over and over again.

Francis Macy, 50, who works in the education field, said he came because he felt like celebrating. "The weather, the time of year made me want to celebrate, and I was feeling loving," Macy said. "I was just standing here and thinking about when Martin Luther King was talking about his dream not too far from here . . . I was taken by the dance with death that they were just singing about. I had forgotten about the ironies of 'Hair.' It still has a strong message, and not just as a memory. The world is still full of violence."