Legalized abortions have reduced abortion-related disease and death among American women and have reduced the incidence of teen-age marriages and out-of-wedlock births significantly, according to a never-delivered statement from a National Centers for Disease Control official.

The 11-page statement, prepared by Dr. Willard Cates Jr., chief of abortion surveillance at the CDC in Atlanta, was to have been given as testimony May 20 before a Senate Judiciary subcommittee.

But his superiors, including Health and Human Services Secretary Richard S. Schweiker, decided to replace Cates at the hearing with another CDC official, Dr. Carl W. Tyler, who presented a three-page report omitting most of the favorable effects of legalized abortion described by Cates.

Schweiker is an opponent of abortion and a longtime advocate of a constitutional amendment to prohibit the procedure, as are his two top health officials, Assistant Secretary Dr. Edward Brandt and Deputy Assistant Secretary Dr. C. Everett Koop. Koop also is Schweiker's choice for surgeon general, a position that would put him in charge of programs administered by the CDC.

Cates' statement would have been given to the subcommittee, which, in an unprecedented anti-abortion vote Thursday, said human life starts at conception. In the statement, Cates said that legal abortions have produced a dramatic decline in abortion-related illnesses and have created new means of "convenient, low-cost delivery of out-patient health services" to women. He also quoted data showing:

In 1965, when abortions were illegal everywhere in the United States, there were 235 abortion-related deaths nationwide, 20 percent of all pregnancy-related deaths, and "it was not unusual for half of all beds in the gynecologic units of large public hospitals to be occupied by women suffering complications" of illegal abortions. In 1976, three years after the Supreme Court decision legalizing abortion, there were two abortion-related deaths.

Advances in surgical methods have made abortion safer than childbirth. "The risk of dying from induced abortion during the first 15 weeks [of pregnancy] is one-seventh the risk of dying from pregnancy and childbirth."

Legal abortion has helped produce significant declines in teen-agers' "high-risk marriages" that often produce unwanted children and has been associated with a decline in out-of-wedlock births in some states. The highest teen-age child-bearing rates occur in states with the lowest abortion rates, the statement said.

The availability of amniocentesis -- examination of the fetus during pregnancy -- and abortion if the fetus is deformed apparently has led to 10 percent more child-bearing, rather than less child-bearing, in families with genetic risks. The indication is that mothers have less fear of becoming pregnant because of these procedures.

Cates' statement concluded that legal abortions had an important and largely favorable public health impact, and that making abortions illegal would result in "a predictable increase in illness and disease of American women."

The decision to replace Cates with Tyler was made in "the office of the secretary," some HHS sources said late last week.

Dr. William Foege, CDC director, acknowleged that he talked to "quite a few people," including the secretary and people in his office, "and he either approved or concurred." But Foege said that the change in officials "was my recommendation and not something someone else asked me to do."

Some sources said that top CDC officials feared that Cates' testimony before anti-abortion senators might have an adverse effect on CDC or its data-gathering, but Foege maintained that the recommendation had nothing to do with any such fears or with any CDC policy.

Tyler is assistant director of CDC's Center for Health Promotion and Education and in charge of all family planning.

"We were uncertain what the committee wanted," Foege said. "I felt Tyler would be prepared to give broader information. Finally our conclusion was, 'Let's go in with the shortest statement we can and see what the questions are.'"

Sen. Max Baucus (D-Mont.), who had asked Cates to testify and who voted against the new "human life statute" last Thursday, said he called Schweiker and asked him to reconsider and have Cates testify. Baucus said his impression was that Cates was considered "too pro-choice, and he was replaced by someone to, in effect, dilute the effect of his probably testimony."

Cates said last week that he has no complaints: "I can live as a scientist with the idea that the administration chooses its own spokesman in the political arena. I have had no restrictions at all on what I want to say in the scientific arena. And we have been very free of an inhibiting influences on the data we collect."