When the Virginia legislature is not in session Sen. Charles L. Waddell will most often be found in a red blazer at Dulles International Airport, where he works as a $20,000-a-year airline representative, or singing bluegrass songs at home.

It is just this kind of unconventional informality, he says, that makes him an effective voice for the citizens of Loudoun and Western Fairfax counties. "I suppose you could consider me a self-styled populist," says Waddell, 47, a Democrat. "I can offer an understanding of the little problems."

But Waddell's colleagues in Richmond say his unorthodox, maverick approach to government is the biggest single reason for the third-term senator's reputation as the state's least effective senator -- an accolade given him last year in a Norfolk newspaper's survey of legislators, state officials, lobbyists and Capitol reporters.

"He always wants to fight the establishment all by himself, whether it's justified or not," says one fellow senator. "I know we sometimes need someone who is willing to be the cutting edge of the Senate, but he's a pretty blunt cutting edge."

In a legislature largely peopled by lawyers and landholders, the high school-educated Waddell has carved out a niche for himself as an affable Don Quixote who is not always taken seriously by his colleagues.

Fellow senators still shake their heads in dismay at memories of Waddell's ill-fated attempt four years ago to wage a one-man filibuster against a resolution favoring the supersonic Concorde.

Now, they say, Waddell is up to his old tricks with his proposals to fill a vacant juvenile court judgeship for Loudoun, Fauquier and Rappahanock counties.

First Waddell used his position to nominate his old friend, Republican Kenneth Rollins, the mayor of Leesburg, for the job. That aroused the ire of the legislature's Democratic leadership and particularly irritated three Democratic delegates from the area who had been challenged by Rollins in last fall's election.

Waddell's move snarled an attempt by those three delegates, Karl E. Bell, David G. Brickley and Floyd Bagley, to put forth Rappahannock lawyer A. Burke Hertz, a Democrat who has own the backing of the Loudoun County Democratic Committee.

The ensuing legislative tangle forced legislators into exraordinary sessions last week in an attempt to smooth things out, and resulted in a rule change that effectively ended Rollins' changes of winning the judgeship.

Undaunted, Waddell still refused to support Hertz because, he said, the lawyer does not live in Loudoun County, which generates most of the cases heard in the 20th judicial district. Waddell offered Leesburg lawyer George Martin instead.

It now appears that what began as a small squabble has irritated almost all of the legislators here in Richmond.

"He's putting us in a intolerable position," said one senator. "You just don't interfere with the selection of judges in Virginia."

Waddell, who with his wife Marie runs a "mom and pop" Senate office in Richmond, readily admits he could be undercutting his own already tenuous position in the Senate through the judgeship struggle.

He insists, however, that his actions are intended as a protest against what he sees as an inequitable judge selection process in Virginia. Under the present system, legislators are bound toecho the vote of their party caucuses. The result is a dearth of Republican judges in the Democrat-dominated state.

"It's worth the fight," Waddell said, near tears, "because if you don't stand up for your principles, what's the use of being here?"

Seen as both an enigma and an outsider in the exclusive Senate club, Waddell has been an effective votegetter back home in his relatively affluent, well-educated district.

In a primary battle last year, Waddell decisively dumped former Fulbright scholar Ray Vickery, garnering about 60 percent of the votes.

Waddell's overall support in his home district seems to have waned somewhat in recent years, however. He squeaked into the current legislative session with only 51.3 percent of the votes cast, compared with the 55 percent he snared in 1975.

Waddell has come a long way from the home that started him on his path as Northern Virginia's urban populist. Born in Braselton, Ga., Waddell was the son of a cotton sharecropper and worked part time as a janitor for two years before graduating from high school. Economic pressures kept him from going to college -- something he still regrets.

"If I'd had the opportunity to go on to college and law school, I could have done as well as some of my colleagues," he says wistfully. "Maybe I could have been rich and maybe even a member of the establishment." He still considers working toward a degree at George Mason University.

It was in Georgia, Waddell says, that he picked up the unique singing style that he has used to entertain state Democrats with his own renditions of the "Howell Cannonball," in honor former lieutenant govenor Henry Howell.

Waddell recorded the tribute to his political mentor during Howell's unsuccessful 1973 gubernatorial campaign. Even now he can readily sing all the words to the flip side of the single that stayed near the bottom of Richmond's charts: a song called "There's a Star-Spangled Banner Waving Somewhere."

Waddell's wife, who is often seen around the state capital in polyester knits, wire-rimmed glasses and jewelry bought from an Avon lady, stands in stark contrast to some of the mink-clad wives of the other senators. She claims credit for running Waddell's Senate office, and many in Richmond see her as providing the real political brains behind her husband.

"She does take to it [politics] more naturally than I do,' Waddell admits.

Colleagues of Waddell, while they occasionally snipe at the Loudoun Democrat's lack of higher education, tend to see his problems as deeper than that.

"He is brainless," said one Northern Virginia delegate, pointing to the dispute over the 20th District judgeship as an example. "If my senator tried to pull something like that on me, I'd look for someone to run against him or I'd run against him myself."

Other legislators say Waddell has no sense of timing, and can't make reasonable compromises with other senators.

"He's always getting up and making some inappropriate remarks that he intends to be funny." said a longtime Waddell watcher. But everybody just groans."

A survey by the Norfolk Virginian-Pilot ranked Waddell as least effective of the 39 senators at last year's session. "The only way he didn't come in last," said one senator who said the vote was accurate, "was that the other senator -- the 40th -- died."

Still, some legislators readily point out that the Loudoun Democrat is viewed as a sincere and hard-working.

"He's an honest, down-to-earth guy," says Sen. Wiley Mitchell (R-Alexandria). "I don't always trust his judgement, but I trust his motives."

"Charlie's greatest asset is that he has a unique ability, when he doesn't understand things, to ask questions," Mitchell said. "Instead of standing up like the captain of a Roman legion, he's willing to listen to advice."

Waddell says his chief legislative victories have been in the areas of land-use planning, environmental protection, transportaion and auto repairs. Largely as a result of his efforts, he says, Loudoun and Fairfax counties have won miles of hiking and biking trails.

In talking about his performance in richmond, Waddell most often turns of themes of trust, honesty, and battling for the underdog.

He pulls a pocket-sized campaign flyer out of his wallet to emphasize the point. It reads: "People stand by Charlie Waddell because he stands up to the special interests lobbysts and the big utilities. He votes his conscience. That attracts political adversaires, but also accounts for a lot of friends. Maybe that's why he's never lost an election."