Dr. C. Everett Koop, President Reagan's controversial nominee to be U.S. surgeon general, yesterday tried to disarm his critics by openly disagreeing with the administration on a critical health issue and pledging he would not use his post as a "pulpit" for his opposition to abortion.

Koop said he has told Health and Human Services Secretary Richard S. Schweiker, "I've said enough and written enough" about abortion.

"It's not my intent to use any government post as a pulpit for ideology," he continued. "It's not my intent to be a speaker on the pro-life circuit as I have been in the past."

A few moments later, Koop, a prominent Philadelphia pediatric surgeon, told a confirmation hearing "as a physician there was no doubt in my mind" that the Reagan administration should have supported a new international code to curb promotion of baby formula in developing countries. The administration opposed the code.

Declaring he plans to be an advocate for the handicapped and elderly, Koop conceded Reagan's budget cuts will "unfavorably impact" those two groups.

The hearing before the Senate Labor and Human Resources Committee was to some extent a day of vindication for Koop and it appeared he will be confirmed easily when the panel votes on the nomination the week of Oct. 12. For months, he has fumed quietly as he has been condemned by feminists, public health officials and editorial writers for his outspoken views on abortion and his alleged insensitivity on women's issues.

Yesterday was the first time Koop has had a public forum to answer his critics, and he clearly relished the opportunity.

The hearing was stacked in favor of Koop, who as chief of surgery at Philadelphia's Children's Hospital, became one of the nation's leading opponents of legalized abortion. Twelve of 14 witnesses, including medical colleagues and two state health officers, testified in support of his nomination. They heaped praise on his compassion, professional skill, dedication, and pioneering medical spirit.

In addition, the Reagan administration, which selected Koop on the advice of several anti-abortion groups, distributed a 29-page report on his background. It credited him with helping identify cancer as a major health problem for children, reducing infant mortality, developing a host of health programs and facilities in Third World nations, and helping rid the United States of X-ray machines used to fit children's shoes.

Sen. Edward M. Kennedy (D-Mass.) grilled Koop on statements he has made criticizing feminists and saying that poverty can bind families together. In one, the pediatric surgeon told a high school graduating class "it is harder to be a woman today that when I was your age" because at that time girls "did not have a feminist telling them they must be liberated and they have to fight for their rights."

Koop said he was just trying to give a little fatherly advice about "the beauties of being a woman, the wonders of being a parent." The crowd loved it, he said. "Some prominent feminists in Philadelphia were on their feet applauding."

The National Organization for Women and the American Public Health Association opposed Koop's nomination. NOW vice president Jane Wells-Schooley said Koop has a "complete lack of understanding of women's rights," holds "extremist views against amniocentesis and abortion," and opposes certain types of birth control. William H. McBeath, APHA executive director, said his group opposes Koop because he lacks training or experience in public health, as is required by law.