Jean Redpath is working her way through the Robert Burns songbook much the way Ella Fitzgerald did for a host of American songwriters. The great Scots traditional singer, a frequent guest on "A Prairie Home Companion," is providing definitive documentation of the great Scots poet's unique musical contributions by patiently recording all 320 of his songs, frequently rematching lyrics and tune variants as Burns intended. The fifth volume of "Songs of Robert Burns" is about to come out on the Philo label, and, Redpath estimates, the final total will be about 20 albums, "give or take three or four."

Burns' song cycle was, according to project director Serge Hovey, a labor of love and cultural pride. "His musical abilities and ear for country music grew year by year. He acquired the ability to read printed melodies from tune collections and write accurate musical notation. He practiced the violin but did not attempt to develop his skill beyond the ability to play strathspeys and slow airs." Burns, who took pleasure in describing himself to friends as "a fiddler and a poet," was a champion of traditional Scots culture as expressed through song, though he was reportedly not much of a singer -- more of a hummer.

Repdath, who will perform at the Commerce Department's Auditorium Friday, is a marvelous singer, with a rich, lustrous voice that has often been compared to a living cello. Recording the Burns opus in such detail has caused a minor controversy, she says. "A lot of folk are devoted to Burns as they learned him in school, and one of the problems we're running into is that the popular songs are frequently sung to melodies that he didn't intend. If somebody learned that as a kid, especially from Aunty Nan or Uncle Hugh, they're not terribly anxious to change their minds later on. So we run into a kind of proprietorial hostility at times about a nice song that has the wrong tune."

A similar problem arose on Redpath's most recent album, a collection of Scottish songs arranged chamber-music style by Joseph Haydn. "It was a spinoff from Burns," she explains, "because quite a few of the songs on that record Burns had a hand in. Haydn is part of a long-term attempt by Scots to 'improve' their music by anglicizing or rendering it more palatable to classical ears.

"That hasn't changed very much in three or four hundred years," she adds with a laugh. "What it did do was give the songs a second crack at life, which was what Burns himself was trying to do -- pick a good melody and put good words to it, so that there were two chances it would survive."

Not surprisingly, Redpath, who commutes between the United States and Stirling, Scotland (where she teaches traditional singing at the university), is considered a leading authority on her country's musical heritage. Still, she's quick to point out that "I grew up with television, radio, record players coming at me, so traditional folk music was not fed at me in a pure form at all. My mother has a remarkable memory for everything, including Victoriana and the popular song of her own day, so I just absorbed a lot. It wasn't something that I chose, it was something that was always there and just gradually evolved. After about 10 years, I realized I wasn't doing this for fun, it was what I was about."

She is constantly on the concert trail, usually traveling alone ("the material is an unaccompanied tradition in Scotland"), and has a deep well of material to draw from. "I don't work with a program," Redpath says. "I have no ideas what I'm going to do when I stand up, but it kills the repetition factor stone dead. If I'm bored, everybody's bored."

How many songs does she know? "I usually call it a thousand, but what do you mean when you say you 'know' a song? I'm sure I 'know' a thousand songs, but I could probably only sing you a chorus of some. I once went for a week without repeating myself, though I was pushing a bit at the end as far as stuff that was fit to perform on the stage.

"I was just playing a game with myself. Mostly I have fun. My main objective is that people shouldn't be sorry that they've come," she adds with a laugh. "Anything goes."