After a full morning of Washington monuments, the high school class from Kansas was less interested in the White House than the woman standing before it.

"Is she for real?" asked one 17-year-old, joining a semicircle of tourists around the woman with a basketball-sized wig and a banner emblazoned with photographs of her body.

The woman, protesting what she calls the government's indiscriminate "gassing and radiating," is one of a corps of Washington complaintants who have adopted the White House's Pennsylvania Avenue sidewalk as a stage of last resort. For thousands of tourists, these cause-driven protesters are often the most memorable part of a visit to the nation's capital.

"The White House sidewalk is a place for all seasons and all reasons," says George Berklacy, the spokesmen for the National Park Service which is responsible for the sidewalk and Lafayette Square across Pennsylvania Avenue. "There are some pretty good shows going on over there. I guess it's really off-Broadway."

The Park Service issues between 750 and 1,000 permits each year for groups that want to demonstrate in front of the White House for -- and against -- a mind-bending variety of causes. In the past five years there have been demonstrations by "Strippers for Christ," "Dykes and Tykes" (a group of radical lesbian mothers), opponents of fluoride, nuclear energy and evolution.

Individual protesters need no permit. They just appear one day with signs and other props for performances that are sometimes amusing and most often sad.

"I guess the longest running show we've had in recent memory was a chap who was there from 1970 until 1977," says Berklacy, who remembers the man was generally opposed to women, marriage and alimony in that order. "The last time we saw him, he was on his way to New York with a woman he met here. I guess he succumbed."

Another favorite of the Park Police and the uniformed division of the Secret Service, which guards the territory inside the White House fence, was the woman who wore sandwich boards which were blank. To the curious who asked about her cause, she would snap: "None of your business."

There are two "pigeon men" who regularly frequent the White House sidewalk, attracting flocks of birds and groups of children. One is a newspaper vendor who says he just likes to feed pigeons. The other is a 61-year-old man who feeds the birds while waiting for President Carter to uncover the "Nazi infiltration of the electronics industry."

Unless they appear to be a danger to themselves or others, police say, the White House protesters are left alone. Between 75 and 100 others are sent each year to St. Elizabeths Hospital in Southeast Washington for mental examinations.

"Generally the ones we get are considered to be paranoid schizophrenics," says Dr. Eugene Stammeyer, the associate director for psychology at St. Elizabeths. "Their delusions are generally persecutory . . . and highly organized."

The woman, whose wig and banner are particularly unusual, seems nevertheless typical of the individuals who regularly frequent the White House sidewalk, says Dr. Stameyer. On any day, in any season, there may be just one person stationed there, or as many as eight, according to police.

The trek to Washington by men and women with causes to champion or delusions to endure is not new, says Stammeyer, who has a newspaper article written in the 1890s which profiles a group of White House supplicants. All fit neatly into current personality profiles of paranoids.

"What's so typical of that group is that they will deprive themselves of basic creature comforts, they'll eat out of garbage cans and sleep in the streets, in order to pursue these delusional beliefs," Stammeyer says.

The current individuals who advertise their suspicion and persecution in front of the White House, snicker at the suggestion that they are deluded.

"Some people say I'm crazy, others call me a Communist . . . but I know the truth," says a woman whom police call the most popular current attraction in front of the White House.

Originally from Spain, the woman says she lives in the street on cunning and $62 a month in food stamps. Most of her belongings are stored in an Alexandria warehouse and most of her nights are spent in carefully selected pay toilets.

Like other D.C. protesters her life is consumed by her cause: trying to halt the constant radiation and gas attacks that are being perpetrated by forces the 40-year-old woman can narrow down no further than "they."

"She's a brilliant woman and an extremely kind woman," says a Washington free-lance writer who hired her to live in her house and baby-sit with her infant child of six months."Obviously she has an emotional problem, but she has a real gift with children."

The woman says she left the sanctuary of that home last year when the radiation became too intense.

To a suggestion that she avail herself of the local missions for homeless women, the woman answers that they are not meant for her.

"Those places are for bums and shopping cart women. They are for crazy people," she says as the tourists on Pennsylvania Avenue stand and stare. "All I want is justice. I just want to start my life again, to be like I used to be."