Among the guests in the presidential box at the Kennedy Center Opera House a couple weeks ago was a congressman's wife taking notes on the physical layout with the intent of committing murder.

Kay-Kay Sharp already has murdered victims in a White House men's room, the substerranean crypt under the Capitol Rotunda and a Capitol Hill restaurant. She also has managed to kidnap the president's daughter and confront a treasonous CIA official in the labyrinthine ruins of Knossos.

All these diabolical schemes have been plotted in a quiet, sunny corner of an enclosed porch of a suburban Arlington home by a lively woman with incredibly blue and innocent eyes.

In the midst of corpses, treachery and intrigue, Kay-Kay Sharp has been having great fun concocting plot surprises.

And apparently the fun is shared by the readers of her first novel, "Sunflower," a non-serious spy thriller that has sold nearly 50,000 hardback copies, brought $500,000 for the paperback rights, been selected by two book clubs and is being considered for a movie.

"It's fun looking for places to kill off people," Sharp says with a smile.

"it's fun looking for places to kill off people," Sharp says with a smile.

There was the time she and her husband, Indiana Rep. Philip Sharp, now in his third term, were invited to the White House for a social function.

"I was concerned about a killing for the 'Sunflower' plot. It has to occur in the White House," Sharp recalls. "The restrooms seemed to be the only place where you could escape the eyes of the Secret Service or the social aides. So I sent Phil into the men's room See SHARP, B6, Col. 1 SHARP, From B1 and told him to notice details and not to come out and just say the room is square."

So, with a little help from the Democratic congressman, a White House murder was plotted.

At the cluttered desk at the backyard end of her sun-lighted porch office, Sharp talks cheerfully about new treachery and murder. She's at work on her second book, which the publisher "optimistically believes is halfway done."

Scattered over the floor are blocks left by Jeremy, her 3-year-old son. A neighbor, with baby daughter in arms, is leaving. Over coffee cups, the talk turns to liquidation of enemy agents and dirty tricks.

"The new book doesn't have Richard Owen the hero of 'Sunflower'," Sharp says with a trace of regret. "I've had requested for his return and want to go back to him in another novel. Richard Owen has to be completely in charge. If there is any luck involved, he has created it.

"It was difficult for me to keep up with Owen's ingenuity. I sat there in the living room staring into the fireplace for three hours before I could figure out a way for Owen to kidnap the president's 4-year-old daughter and make his escape."

It would be treason to reveal such secrets in a thriller that piles up one surprise atop another to a corker of a conclusion.

"One reviewer had a body count of 25," Sharp noted. "I know there aren't that many. Some murders you only hear about and are not described on the spot."

Such a body count would be unfair to "Sunflower," which doesn't dwell on violence but dazzling plot twists as Owen, a loner and CIA agent with a selective amorality unravels a cunning scheme involving the president, the CIA director, foreign spies and treason in high places.

"I'm not trying to reflect the reality of spy work or philosophize about the moral issues," Sharp emphasizes. "I'm not Graham Greene or Le Carrer. I write for fun and entertainment and for escape.

"I know a few people who work at the CIA-not agents in the field," the author says. "They said they had fun reading it. I'm naive about spy operations. I read a few books with such details as how difficult it is for secret agents to file for medical benefits for work injuries."

The seed for "Sunflower" goes back 20 years or more, long before the author came to Washington in 1974 as the wife of the congressman. She remembers "reading my way through the Muncie (ind.) library" and coming upon Graham Greene's "The Ministry of Fear."

She started taking notes on overheard conversations, people's faces, plot ideas, descriptions of places. The notes fill boxes stored in the basement of the Sharps' Arlington home.

The note-taking continued through DePauw University and a job as a researcher at the New Yorker magazine after graduation in 1963.

"The closest that I ever came to Katharine White (the New Yorker's late fiction editor and discoverer of literatary talent) was when friends came to town and I would go to Mrs. White's empty office," Sharp recalls.

"I would spread galleys over the desk and pretend to be talking on the phone to J. D. Salinger when my friend was brough in."

Even then, Sharp remembers, she must have been serious about writing a book. A few jobs later, she quit to try. In 1972, she worked in the campaign of a former political science professor at Ball State University. Phil Sharp lost that campaign but married Kay-Kay that fall. In 1974, the Sharps tried again and won the congressional seat.

Sharp candidly concedes that being a congressman's wife didn't hurt when she was looking for an agent and a publisher.

"Of course, there is the peg for promotion in the author being a congressman's wife," she readily admits.

But before that were all those years of note-taking and plot scheming and then the long hours at the typewriter on the Arlington porch.

In "Sunflower," Vanessa, wife of the CIA director, muses why "so many men who stump the country defending women's rights still think Washington wives have no existence apart from them."

Kay-Kay Sharp feels that her writing offers a good arrangement for a combination of careers with her husband:

"In Washington, people's worth is measured by power and not so much by money. The value of work is considered. What Phil is doing as a congressman is so much more important than what I do. I don't mean to scoff at offering entertainment. But what Phil is doing is so much more important."

Still she is not scoffing at the half-million (I don't get all that, you know") for the paperback rights of her first novel.

This afternoon at 4:30 Tip O'Neil will give a reception for Sharp in the Speaker's dining room at the Capitol.

She'll probably go home and jot down some notes.

It's a nice place for a murder. CAPTION: Picture 1, Kay-Kay Sharp, by James M. Thresher-The Washington Post; Picture 2, Kay-Kay Sharp, by James M. Thresher