What do you call a congressman from a rural, conservative region of Texas who earns his constituents' outrage by supporting aid to that wicked city of New York? And who rubs it in by escorting Mayor Edward Koch to his home district as an honored guest?

Around Capitol Hill they call Representative Charles Wilson "Good Time Charlie," in recognition of his boisterous, good-natured approach to government that doesn't preclude tweaking his public a few weeks before he asks to be reelected.

"I've taken more criticism for my vote for aid to New York, and I just decided to jam it in their ear," says Wilson, 45, with a huge smile. "I'm making Eddie the honorary admiral of Toledo Bend Reservoir."

Koch's apperance - he and Wilson became fast friends when they traveled together to Israel after the Yom Kippur War - was late last month, at a Wilson fund-raiser over which Walter Mondale presided. The gesture kept with the style that's come to be expected of the lean, 6-foot-4-inch congressman with the jutting jaw. He went against the grain of his district by backing the Panama Canal treaty. His pro-abortion stand is controversial. And some pundits wonder how his $40,000 investment in the flashy K Street club called Elan plays back home, where Deep South traditions mark the largely blue-collar population that keeps Wilson in Washington. Still, he faces no problem getting reelected this week.

"I've never sacrificed the way that I wanted to live for mores that other people perceive of my district," answers Wilson. "My constituents know they're not electing a constipated monk. A lot of Southern politicians are hypocritical and pious, and they don't need to be."

Or they shouldn't be, Wilson might add; his predecessor, John Dowdy, was a conservative, Southern traditionalist who was convicted in 1972 on federal bribery charges. Wilson, then a state senator, easily beat Dowdy's wife in the Democratic primary. To hear Wilson tell it, it's been one big party ever since.

"I have an enormously good time," he says. "There's nothing about his job I don't like. I'm a legislative animal. You can take a job seriously without taking yourself seriously, and I think the fact that I go around without a frown all the time (puts out) some people."

Wilson is known as a tough legislator who elbowed his way onto the appropriations committee. More recently, he held some of the president's legislation hostage until the administration saw things his way and agreed to release some foreign aid to Nicaragua despite that country's reputation at the State Department for violating human rights. (On that last point, Wilson talks tough: "I decided the next time the left-wing exotics tried to slap around one of our conservative allies, I'd fight. And I did.")

He prospers by virtue of enormous personal charm, say those who know Wilson. Unlike some reclusive colleagues, he's established personal relationships with other members. He's known as a charmer - his office staff is renowned for its beautiful (and professional) women. He says he wanted a piece of Elan, he told the Texas owners, "because I'm up here and I can tell if the glasses are clean and the waitresses pretty." He often parties there with his wife, a Capitol Hill real estate agent he married in 1963.

He admits to occasional bouts of depression, "maybe because I'm up so much . . . I withdraw then, I like to be alone. But I wouldn't swap this job for anything. It's a great adventure, a great game. I love a parade. Like someone said, 'If it's a funeral, I want to be the corpse; if it's a wedding, I want to be the bride.'"