The text of his letter was released late Sept. 21 by the U.S. Conference of Catholic Bishops. There was no immediate response from the White House to a Sept. 22 request from Catholic News Service for comment on the archbishop's letter.

Dolan underscored the Church's position recognizing "the immeasurable personal dignity and equal worth of all individuals, including those with same-sex attraction," and said "we reject all hatred and unjust treatment against any person."

But he called for dialogue with the president on the Defense of Marriage Act and the "definition of marriage as the union of a man and a woman."

"I am convinced that the door to a dialogue that is strong enough to endure even serious and fundamental disagreements can and must remain open, and I believe that you desire the same," the USCCB leader wrote.

He predicted that the administration's actions in relation to the Defense of Marriage Act would "precipitate a national conflict between Church and state of enormous proportions and to the detriment of both institutions."

He said the administration's decision last spring not to defend DOMA in court was "problem enough, given the duty of the executive branch to enforce even laws it disfavours." But now the Justice Department "has shifted ... to actively attacking DOMA's constitutionality," he said.

In addition to the two-page letter, Dolan sent Obama a three-page analysis prepared by USCCB staff on "recent federal threats to marriage," including a White House official's comments in May indicating that Obama supports imposition of a federal mandate to "ensure adoption rights for all couples and individuals, regardless of their sexual orientation," and a directive in April from the Office of Navy Chaplains requiring access to Navy chapels for same-sex wedding ceremonies. The Navy suspended the directive in May, "but did not reject it outright," the analysis said.

"The administration's efforts to change the law — in all three branches of the federal government — so that support for authentic marriage is treated as an instance of 'sexual orientation discrimination,' will threaten to spawn a wide range of legal sanctions against individuals and institutions within the Catholic community, and in many others as well," the analysis said.

"Society will suffer," it added, if religious institutions are compelled to end participation in the social service network "due to their duty to maintain their institutional integrity and not compromise on basic moral principles."

The analysis noted that Obama himself had commented on "the indispensable role of both mothers and fathers" in his 2011 proclamations for Mother's Day and Father's Day, which "appeared to affirm on the president's part that neither a mom nor a dad is expendable."

Dolan told Obama that his letter "reflects the strong sentiments expressed at a recent meeting by more than 30 of my brother bishops" and shared by "hundreds of additional Catholic bishops throughout the nation."

"The Catholic bishops stand ready to affirm every positive measure taken by you and your administration to strengthen marriage and the family," he said. "We cannot be silent, however, when federal steps harmful to marriage, the laws defending it and religious freedom continue apace."