In his closing comments at Yesterday's news conference, President Reagan suggested he supports a relatively obscure but controversial piece of legislation intended to establish, without constitutional amendment, that abortion is illegal.

Reagan indicated that he favors a bill declaring that human life begins at the moment of conception. If the bill passes, abortion would be the taking of human life, and thus a crime. Opponents of the legislative definition of life argue, among other things, that the bill is a "back-door" attempt to infringe constitutional rights, and also say that the bill would outlaw some of the most commonly used forms of contraceptives, including the intrauterine device (IUD).

The legislation was introduced in January by three leading congressional foes of abortion, who admit that the bill is an attempt to circumvent the 1973 Supreme Court opinion that voided most laws against abortion. Normally it takes a constitutional amendment to reverse a Supreme Court ruling based on constitutional law, as was the 1973 opinion. Abortion opponents in Congress apparently cannot garner the two-thirds majority required to submit an amendment to the states for ratification. But the foes of abortion think they effectively could nullify the 1973 decision with the bill, which would require only a simple majority vote in Congress.

When asked about the legislation at the end of his news conference, Reagan specifically supported this aspect of the proposal. Once it is determined that the unborn fetus is a human life, Reagan said, "there really isn't any need for an amendment because once you have determined this, the Constitution already protects the right of human life."

Reagan noted that Congress will hear testimony from "medical authorities, theologians, possibly legal authorities" on the subject. But he reiterated his support for a ban on abortion. Since there is no certainty as to whether or not a fetus should be considered a human life, he said, "I think that everything in our society calls for opting that they might be alive."

Asked about the effects of the bill on contraception, Reagan said he does not oppose contraception. But when asked for further elaboration, he simple repeated his explanation of why he opposes abortion.

Supporters of the proposed legislation took the president's comments as an endorsement and an important asset in their efforts to win its passage.

"This means the bill's going to become law," said Carl Anderson, legislative assistant to Sen. Jesse A. Helms (R-N.C.), a sponsor of the measure. He said the president's comments would give the legislation priority among the hundreds of pending bills in Congress and would tend to answer suggestions from some Republicans that Congress put off work on such social issues as abortion until it has completed work on Reagan's economic program.

The bill's legislative path will begin in the Senate, where anti-abortion Republicans control the Judiciary Committee. Sen. Orrin G. Hatch (R-Utah), chairman of the subcommittee on the Constitution, and Sen. John P. East (R-N.C.), chairman of the subcommittee on separation of powers, tentatively have scheduled joint hearings in April on the bill defining human life, and on other abortion legislation.