BALTIMORE -- Cardinal Francis George told the U.S. Conference of Catholic Bishops yesterday to rejoice that the nation has changed enough to elect a black president, but he drew parallels between the laws that once made slavery a right and those that make abortion a right.

"The common good can never be adequately incarnated in any society when those waiting to be born can be legally killed at choice," the president of the group said to long applause from nearly 300 bishops gathered here for their regular meeting.

"If the Supreme Court's Dred Scott decision that African Americans were other people's property, and somehow less than persons, were still settled constitutional law, Mr. Obama would not be president of the United States. Today, as was the case 150 years ago, common ground cannot be found by destroying the common good."

In 1857 the Supreme Court ruled, 7-2, that Dred Scott, a slave who had lived with his master in free states, could not be free after his master died. It declared that no slave or descendent of slaves could ever be a U.S. citizen.

Opponents of abortion draw parallels between that case and Roe v. Wade, the 1973 decision legalizing abortion.

"We must all rejoice" that the nation that once enslaved Africans has elected a black president, he said. "Pragmatically, we must also hope that President Obama succeeds in his task, for the good of all. The odds against success are formidable."

The bishops support some of Mr. Obama's goals, such as universal health insurance. But they are alarmed by his promise to sign the Freedom of Choice Act, which would abolish restrictions on legal abortion and require health providers -- including Catholic ones -- to offer the procedure.

"We are particularly concerned with the freedom of conscience of health-care workers and the Catholic health-care system," he said, saying Catholic institutions provide at least one-third of all health care in Illinois. "They stand as witnesses to the world that there is someplace in our society where no one is deliberately killed."

The Obama team has indicated that he may quickly overturn the Bush administration's ban on the destruction of human embryos for stem-cell research.

Archbishop Donald Wuerl of Washington, D.C., urged caution. "I would hope that on issues as significant as defending and protecting human life, there would be no precipitous action to change where we are in public policy. That should really be something that reflects a great deal of thought, conversation and reflection," he said.

The archbishop, who has been a guest at the White House several times since his 2006 appointment, said it is primarily the task of the U.S. Conference of Catholic Bishops, not individual bishops, to address public policy issues.

Bishop David Zubik, Archbishop Wuerl's successor in Pittsburgh, praised Cardinal George's speech for what it said about positive change in race relations and for drawing the connection to abortion. Shortly before the election, Bishop Zubik had written that opposition to abortion should be the paramount issue.

Since Mr. Obama won, he said, "I'm hoping that there will be more of a middle ground," rather than winner-take-all on the issue.

Cardinal George said that October's economic collapse made the economy the top issue for the majority of voters, Catholics included.

He defended "Faithful Citizenship," a document the bishops adopted a year ago to guide Catholics in electoral decisions. It highlighted many issues -- including racism and torture -- that Catholics must care about, but said abortion and euthanasia are the most important because they involve the deliberate killing of innocents. Some conservative Catholics denounced the bishops for giving any importance to other issues, while some liberal Catholics lambasted them for saying abortion was paramount.

"The statement was good. It was nuanced where it should be. The nuance was often lost when different groups took different parts of it ... and stressed one part or the other," he said.

He called for greater unity among Catholics.

"The church and her life and teaching do not fit easily into the prior narratives that shape our public discussions. As bishops, we can only insist that those who would impose their own agenda on the church, those who believe and act self-righteously, answerable only to themselves -- whether ideologically on the left or the right -- betray the Lord Jesus," he said.

"Strengthening people's relationship with Christ remains our primary concern and duty as bishops. We extend that pastoral concern, especially at the beginning of a new administration and a new Congress, to Catholics of either major party serving others in government. We respect you and love you, and we pray that the Catholic faith will shape your decisions so that our communion may be full."