One day after the National conference of Catholic Bishops made public its proposed position on nuclear arms, a key author of the statement last night countered press charges that the Bishops had toned down their stance under pressure from the Reagan Administration.

Speaking before a Kennedy School seminar audience of 40, Rev. J. Bryan Hehir disclaimed recent allegations that the Bishops "curb" for "halt" in a recommendation on the nuclear arms race and stapped up their criticism of the Soviet Union's human rights policy following Administration pressure.

Hehir asserted that most modifications were the result of internal recommendation.

"I'm not terribly happy with how this has been reported," Hehir said, adding that "the Administration has been given credit for many changes it had nothing to do with."

He streased that Administration influence was limited. In response to a series of letters from National Security Council Advisor William Clark. Hehir said, the conference decided to incorporate into the statement a mention of the Administration's commitment to avoid attacking population centers and a reference to the Administration's arms-limitation proposals.

The position, to be released in the form of an open letter, will serve as a guideline for Catholic clergy and congregations.

In an interview following the speech, Hehir said that he did not feel that the Bishops' published proposal--the third draft this year--was a retrenchment on his earlier positions. "I'm quite satisfied with the way it turned out," he added.

The letter will receive final approval at a Bishop's convention in Chicago next month.

There is still a chance of floor reversals on the more controversial aspects of the letter, including its condemnation of any first use of nuclear weaponry and the decision not to adopt the word "freeze," a term popularized by a growing number of secular movements.