President Reagan yesterday endorsed a bill that would prohibit use of federal money for Medicaid abortions for the poor, coverage of abortions in health insurance plans for government workers, research on abortion and population control programs abroad that promote abortion.

The bill, introduced by Rep. Henry J. Hyde (R-Ill.), also says that it is "a finding of Congress that the life of each human being begins at conception" and that the Supreme Court "erred" in its 1973 Roe vs. Wade decision legalizing abortion.

The endorsement, included in a "Dear Henry" letter to Hyde, came on the eve of the 10th anniversary of the controversial decision as Reagan met with anti-abortion leaders at the White House.

The chief purpose of the so-called "Respect Human Life Act" is to enshrine in the legal code prohibitions on use of federal funds for abortion. Hyde has placed riders on appropriations bills annually since 1978 to accomplish the same task, but the measure is more far-reaching than the amendments.

Apparently designed to provide a rallying point for anti-abortion groups, long divided over a legislative approach to abortion, the proposal incorporates elements of a Human Life Bill pushed unsuccessfully last year by Sen. Jesse Helms (R-N.C.). But these elements are included in the bill Reagan endorsed yesterday as "findings of Congress," which do not have the force of law.

The most controversial of these is the finding that "scientific evidence demonstrates human life begins at conception." This is an issue on which there is medical and legal disagreement. The bill also would halt federal funds to any hospital that withheld treatment, even at the request of parents, from handicapped children.

Reagan's endorsement and his meeting with anti-abortion leaders the day before an annual "March for Life" here held an important symbolic significance. Among those invited to the White House was the Rev. Jerry Falwell, the television evangelist and founder of the Moral Majority.

Groups favoring legal abortion, including representatives of major Protestant churches, long have sought a meeting with Reagan, unsuccessfully.

"It happens that we represent the point of view of a majority of Americans," charged Faye Wattleton, president of the Planned Parenthood Federation of America. "Mr. Reagan simply has said that he cares not to hear about their point of view."

She was joined at a news conference by representatives of the American Civil Liberties Union, the National Organization for Women and the Religious Coalition for Abortion Rights. All pledged to fight the new Hyde bill.

Although repeatedly approved by Congress, Hyde amendments have been only partly successful. Fifteen states and the District of Columbia continue to finance more than 290,000 Medicaid abortions each year with nonfederal funds.

Washington yesterday was awash with rallies, seminars, fund-raisers and caucuses of the opponents and supporters of legalized abortion, all gathered to mark the anniversary of the Supreme Court decision.

At one meeting, the board of the National Right to Life Committee unanimously passed a resolution apologizing to Helms, leader of anti-abortion forces in the Senate, for a well-publicized NRLC memo suggesting that he has become so unpopular with his peers that he may no longer be able effectively to champion the group's cause.

Dr. John Willke, NRLC president, said a delegation had been appointed to meet with Helms to express the group's "deep gratitude and appreciation" to him. "Sen. Helms has been the maximum leader of our movement," he said.

The author of the memo, legislative director Douglas Johnson, will continue to work for the organization, he said. The memo, which prompted calls for Johnson's ouster, said animosity toward Helms among his Senate peers had reached "a very high level" and that "the popularity factor" could make the difference between passage or defeat of anti-abortion legislation