The Carter administration will end the "politicization" of the National Institutes of Health, the government's showcase medical research center in Bethesda, Joseph A. Califano Jr., the ne Secretary of Health, Education and Welfare, promised yesterday.

He called the move part of "un-Nixonizing" the hug ecomplex of health laboratories and officials who parcel out more than $2 billion a year to the nation's research scientists.

NIH's work is "too critical a part of the national health care system" to the subject to political control, the new Cabinet member said in his first news conference.

But he would not say whether or not he will keep Dr. Donald S. Fredrickson, a favorite of the scientific community , as HIH director. add one Calofano - N

Califano also announced the start of a comprehensive study of welfare reform to prepare the program, which is to be presented to the White House by May 1.

Califano also disclosed he is requiring a thorough review of HEW's Office of Civil Rights, which he said has been guilty of "too much data collection and too little enforcement." F. Peter Libassi, who was first director of that office from 1966 to 1968, will direct the review.

THe important HIH directorship that Fredrickson holds was first made subject to White House approval in the early Nixon years.

Appointments to NIH advisory committees were subjected to political approval, adn NIH information officers were pressured to write pro-administration material.

President Ford in 1975, named Fredrickson - former NIH heart scientist and head of th prestitigious Institute of Medicine at the National Academy of Sciences - to head the research center. Scietists soon praised him for rebuilding morale.

Asked if he would remove Fredrickson's job from White House approval Califano sais, "I'd like to un-Nixonize anything that's happened in this government."

More specifically, he promised to talk to Fredrickson and make a decision in the Next 10 days. "Whatever happens at NIH," he pledged, "we are ending the politicization of that institution and its advisory committees" because "the work they do is too important, too critical."

The decision of Frederickson may await appointment of a new assistant secretary of HEW for health. Among leading candidates for that position are Drs. Harvey Sloane, Louisville, Ky., mayor; Lesterr Breslow, California public health professro and former California health commissioner; Joseph English, New York psychiatrist and HEW official under President Johnson; Thomas Bryant, another Johnson official who heads the private Drug Abuse Council, and William Roy, for mer Kansas congressman.

All worked in a Carter campaign health task force.

Califano repeated recent statements that the administration would not be ready to send Congress a national health insurance bill this year. But he said this does not rule out action to control health costs and overuse.

Califano said the welfare reform study will start "from scratch" and will investigate every possible avenue for revising the present patchwork system. "I want a serious, continual debate" on the issue, he said.

Henry Aaron, who was recently nominated to be HEW assistant secretary for planning and evaluation, will direct the study. Aaron is a Brookings Institution fellow who has written extensively on tax and welfare issues, including one book on the difficulties of reforming welfare.

Libassi will be charged with finding a way to reorganize the civil rights office, which Califano said is characterized by "ineffective effort." He said the Carter administration will be "vigorously involved" in enforcing civil rights laws for women and minority groups. Libassi, he added, is not seeking an appointment to head the office.