Paddy Moloney is a terriffic advertisement for Ireland: five feet of raucus energy capped by a crescent-shaped profile resolved at opposite ends by an angular jaw and a nose that is . . . prominent. Somewhere in between is a toothy leprechaun smile, a lilting brogue as thick as potato soupo and a stubborn pride in the traditional music of his group, the chieftains.

"Whatever's in Irish music seems to get across to people," Moloney says in the rich tongue that has won friends around the world. Over the years, the Chieftains' infectious enthusiasm has inspired a new respect for their country's traditional music, too often stereotyped as "lusty joy and mournful grace."

"I think we've overcome that," Moloney smiles. "We gave them a different idea of what the music is all about. It's the mission we set out on 20 years ago. It's not 'Mother Macree' and all those other tear-jerkers. It's very joyful." Last week, Moloney sat on the lip of the stage in Madison Square Garden as a special invited guest of the Grateful Dead. "I was fascinated by the whole thing," he says, "It's the first time I've ever seen a Dead concert. I thought they were marrrr-velous."

That's what people have been saying about the Chieftains since they first formed in 1963. Their award-winning film score for "Barry Lyndon" in 1976 first brought them to wide attention in the United States, but they had been voted England's "Band of the Year" in 1975 over Led Zeppelin, the Rolling Stones and other far-better known stars. It was also the year they made the immense decision to pursue music full-time, giving up the security of jobs as engineers, postmen and contracters.

At their Austin Opera House show last week, the Chieftains became honorary Texans and were crowned with the obligatory 10-gallon hats. In return, they threw a rollicking version of "Cotton-Eyed Joe" into their set. r"It's almost identical to one of our reels called 'Did you wash Your Father's Shirt, Did You Wash It Clean,'" Moloney points out, adding that much bluegrass and traditional American music can be traced to Ireland. It's a bond that unites musicians of both countries, sometimes in cramped quarters. "We were on the West coast of Canada and when we got back to the hotel there were 20 musicians bashing away in a room, playing tunes I'd never heard of before . . . it was fan-tas-tic!"

The Chieftains' blend of classical frameworks over folk melodies has made its members very much in demand on other artists' projects, which is how Moloney became the only outsider to be with Paul McCartney the day after John Lennon was killed in New York. McCartney had come to know Moloney through work on brother Mike McGear's album and had finally managed to snag the pint-sized piper for one day between Chieftain tours. On the morning of the sessions, Moloney called from Dublin to see if they were still on and was told to fly to George Martin's AIR studio in London. McCartney arrived early with his wife and children and, according to Moloney, "he was just stunned. He was really upset by it, a situation not helped by all the people jammed outside the studio."

Though McCartney received much criticism for going ahead with the session, Moloney feels that working was the former Beatle's defense mechanism, that the shock was only beginning to settle in. Moloney doesn't even remember the name of the tune or the medoly on which he played some unileann (elbow) pipes and tin whistle."McCartney did give me a standing ovation at the end, the big clap," he adds.

On a happier note, Moloney and his five fellow band members are beseiged not only with tour offers (China and the Soviet Union have both extended official invitations), but with scoring assignments in film, theater and dance. Moloney long ago finished 90 minutes of original music for the Richard Burton film, "Tristan and Iseult," but "it's held up on the length of the film." Other projects include the film version of Thomas Flanagan's "Year of the French," "The Lion of Ireland" by Morgan Llywelyn, which deals with the 11th-century Irish king Brian Boru, who can allegedly claim President Ronald Reagan as a direct Descendant. "We play 'Brian Boru's March' already," Moloney laughs.

In 1979, the Chieftains performed with Pope John Paul II and a chorus of 6,000 in Dublin. The crowd numbered 1.3 million ("Hig gig of course," Moloney says deferentially) and the pope was so impressed that he invited the group to the Vatican during their next Italian tour. "We were asked to play for him at an audience, which we did for three hours, off and on.Afterwards, he spoke to each member of the band for about 10 minutes, gave us each rosary beads. He's a great man, fantastic charisma."

When the Chieftains finish this American tour they'll fly back to Ireland ("for some reason Aer Lingus don't fly on the Patrick's day," Moloney grieves) to be home in time for a special television program hosted by Princess Grace of Monaco. Filmed in Dublin Castle, it will feature music from a mass that Moloney has written and will be broadcast later to 120 countries.

It's that kind of multiple exposure that's allowed "a gradual building up of letting people know what the sound of Irish music is all about," Moloney believes. "It could be the music. People have come around to the concept . . . and it's good fun all the time."

At home, Moloney dreams of a state-supported folk orchestra. "There has been talk of it. There's a state chamber orchestra, a state symphony, a state ballet. We do more for the country than any of them," he says tersely. "They do regard us, of course, as their best ambassadors."

Also at home is the first record player Moloney has ever owned, a Christmas present. "At long, long last," he laughs. "I haven't had a chance to listen to the hundreds of records I've been given. I must get a Grateful Dead record, actually.