Renata Babak and Paul Plishka sang a concert last night under the auspices of the National Fine Arts Foundation. The Kennedy Center program was offered in support of human rights.

Babak is a mezzo soprano, formerly with the Bolshoi Opera in Moscow, who defected from the Soviet Union in 1973.Plishka is one of the principal basses of the Metropolitan Opera.

From the opening notes of his first group of songs by Tecaikovsky, Lysenko, and Rachmaninov, Plishka demonstrated a mastery of the concert stage that equals his command of opera.

His voice has the luster of burnished mahogany, with a free, ringing top that made for real excitement. Calling up wide dynamic shadings, he, assisted by some magnificent playing by pianist Thomas Hrynkiv, made "The Hrvest of Sorrow" and "Floods of "Spring" by Rachmaninov matters of the highest caliber. In John Jacob Niles' gambling songs, Plishka's English was as enjoyble as his Russian.

Babak's voice has a natural opulence about it that puts a real thrill in some phrases. However, she breaks her voice up into divisions over which her generalship is uneven. The low voice, when driven, is hard and chesty. The middle is troubled by a steady vibrato that sometimes becomes far too broad.

In quietr singing, Babak was often appealing. In operatic scenes she drove the sound past the point of agreeableness. In duets with Plishka, his tone was like a solid pillar against which her vocal methods had little chance.

Throughout the concert, Hrynkiv gave continuing proof of his remarkable artistry.