Kathy Coyle is one of the people you meet the minute you walk into a campaign headquarters. She's the one wearing a wool tweed skirt on a blazing hot day, the one with the flat Boston accent in a room of lilting drawls, the one whose car trunk is full of posters and straw hats from a half-dozen political races in as many states.

Coyle is now campaign manager for Reid Hughes, a liberal who is challenging Rep. William V. Chappell Jr. in today's Florida Democratic primary runoff.

Molly Burns is an advertising copywriter from Orlando who hasn't worked for a politician since she passed out leaflets for John F. Kennedy as a teen-ager in 1960. She was drawn into the campaign by a want ad offering $145 a week to "environmental/political activists" willing to work for Hughes and other candidates under the auspices of the League of Conservation Voters.

The league is one of five young political action committees of the environmental movement, and Burns is the sort of campaign novice these groups have coaxed into politics this year.

The campaign has overtones of a "cause" -- a liberal taking on a boll weevil -- and it has lured a subculture of young politicos from across the country, people like Coyle, who hasn't lived in one place for more than four months in the last several years.

At 26, Kathy Coyle is a confirmed political nomad, who has counterparts in dozens of campaigns across the country. She has leapfrogged for years from one Democratic campaign to the next, registering voters in New Jersey, targeting precincts in New Hampshire, now getting out the vote in Florida.

She often packs up her Renault Le Car on a day's notice, spurred by a call for help from a comrade. She rarely has time to go home to Boston to pick up a change of clothes for the change of climate.

"I was told several years ago I was the youngest political hack anyone had ever met," said Coyle, amused and a little disturbed by the label.

Molly Burns has a different background. With her blonde hair in ringlets and her face aglow but slightly worn, she has the look of a woman (39) who is refusing to let time wrest her youth away. She speaks with passion of the threats to Florida's natural beauty as she goes from door to door in the 4th Congressional District.

Each day, it is Molly Burns who recruits more volunteers than most, if not all, the other door-knockers deployed daily by the league.

"Seven! I got seven volunteers!" she exclaimed late one night last week as she returned to Hughes' headquarters, collapsing on an old sofa after a day of canvassing.

Burns is staying with all the younger activists at a rickety motel on the beach, where some rooms smell of insecticide and others harbor roaches. It is obvious that she is not accustomed to such haunts.

Coyle, on the other hand, has stayed in so many places like this that they blur in her mind, and she occasionally wakes up wondering what race and state she's in. Before Hughes in Florida, it was Frank Lautenberg in New Jersey.

In 1980, it was Jimmy Carter all over the East Coast. In 1978, it was Bill Hathaway in Maine and Hugh Gallen in New Hampshire and Sen. Paul E. Tsongas (D) in Massachusetts. She's here for the same reason she worked in all the others -- "fighting the good fight."

For Burns, explanations come harder. She has temporarily left behind a boyfriend and a new apartment "for something I believe in."

She says she is doing it because she cares about the environment. She also says she is fascinated by St. Francis of Assisi, the patron saint of ecology. And she has a college-age daughter who pricks her political conscience.

Molly Burns apparently decided after our conversation that she had not said enough. The next morning, I found a note from her under the windshield wiper of my car. It was written at 12:54 a.m. at the rickety motel.

"You started me thinking: Why am I here . . . ?" the note began.

At last she had figured it out. It wasn't just the environment or politics, she wrote. It was largely the idealism of the young woman who interviewed her for the job.

"She reminded me of my daughter," she wrote. "Listening to her, I thought that perhaps she was naive, then caught myself. All of a sudden, I felt middle-aged and overly 'realistic.' I did not want this young woman to become disappointed or disillusioned. I don't want to be past believing that a group of dedicated people CAN really make a difference.

"A last hurrah as I face 40? Or maybe I would simply like my daughter to be proud of me. -- Molly Burns." Folded inside the note was a small picture of St. Francis of Assisi.