"This country can support only two folksingers at a time, and right now those two are Pete Seeger and Odetta," a Harvard senior said sometime ago, giving up plans to make a living with a guitar and banjo and heading off to the Law School.

Since that time, the West Coast has spawned the Kingston Trio and other so-called "folk groups," Oberlin College gave birth to a prospering folk song and dance act, and Boston has fallen prey to the indisputable economic lure posed by B.U. and Brandeis folkniks. This week two old troopers, Sonny Terry and Brownie McGee, initiated the Golden Vanity, an unconventional coffee-house.

Terry and McGee made their first Boston appearance in the opening offering of the Folklore Concert Series at Jordan Hall and gave a sampling of their repertory at the Vanity. Alan Lomax, America's greatest living folklorist, gave one of his rare public performances and it's too bad he didn't stay around longer. He brought with him a pleasant English girl named Shirley Collins, who sang some ballads in a thinnish voice.

Opening the program with Everybody Loves Saturday Night, Lomax rambled through a couple of Great Lakes ballads, and Range of the Buffalo, displaying the charm which contributed to his success as a folksong collector for the Library of Congress.

In spite of their new-found prosperity, the lame McGee and blind Sonny Terry sing and shout their blues with all the pathos of their poverty-stricken days in Carolina and Tenessee. They began with Midnight Special and Can't Stop Me Now Because I'm Climbing On Top of the Hill, during which Terry, a man with a rhythmic soul, seemed to be singing and playing his harmonica at the same time. Sticking to the tried and true, they followed with John Henry, Take This Hammer and Poor Howard's Dead and Gone, an old Leadbelly song which Terry recorded at the memorable Carnegie Hall Christmas concert with Pete Seeger.

Lomax returned to lead the audience in Almost Done, a song he collected years ago from penitentiaries, when the wardens permitted him to visit with the prisoners and swap songs and stories. Terry and McGee rocked through I Don't Want No Cornbread and Molasses, straight out of a southern jail, and marched out with When the Saints Go Marching In.