A letter from Virginia Sen. Paul S. Trible Jr. asking state high school principals to send students to a Christian prayer breakfast in Rosslyn this weekend has prompted criticism that the Republican lawmaker improperly mixed government and religion.

The letter provoked such a furor that Sen. John W. Warner (R-Va.), who was described in it as a cohost, issued a statement disavowing any involvement in the breakfast and an associated leadership conference. A spokesman said Warner had spoken at the program for two years but never intended to be a sponsor.

Trible's Dec. 30 letter to principals was printed on stationery bearing his official title and signature. "Our purpose is to demonstrate the relevance of Jesus Christ to contemporary life and the power of prayer to impact our lives and the life of this world," it said.

The Virginia chapters of the Anti-Defamation League of B'nai Brith and the American Civil Liberties Union, among others, said Trible's letter gave the appearance of government sponsorship of religion and improperly involved high school principals, who are public employees, in a religious enterprise.

Bob Edwards, a spokesman for Walter F. Sullivan, the Catholic bishop of Richmond, said yesterday that the bishop wrote Trible "not being critical of him but sort of raising the question of being more sensitive to the various variety of beliefs and faiths within public schools."

"It's very divisive and even humiliating to youngsters of other faiths to be left out, for a U.S. senator not to want to include them in something he put his name to," said Robert L. Maddox, a Baptist minister who is executive director of Americans United for Separation of Church and State.

Trible said yesterday the letter clearly stated that it was printed at private expense, and he described the prayer weekend as a "purely private enterprise." It is organized by the Fellowship Foundation, which has helped establish prayer breakfasts nationwide, and more than 400 students are expected to attend the event at the Key Bridge Marriott, the senator said.

In the five years since the program began, "not once has a principal objected," said Trible, a freshman senator who is considering running for governor after he retires at the end of his term this year. " . . . It's obviously not my intention to show insensitivity to anyone. I'm simply living out my faith in my own time and my own way.

"I don't believe that a letter to principals treads on the First Amendment" mandating separation of church and state, Trible said, "but I want to be sensitive to the concerns that have been raised, so in the future public high school principals will not be involved again."

"Don't be too tough on me," he said in ending the interview.