The pope's U.S. ambassador praised American bishops Wednesday for confronting the government over religious liberty issues, including resisting the mandate from President Barack Obama's administration that health insurance cover birth control.

Archbishop Carlo Vigano, the papal nuncio based in Washington, noted that the advocacy required a "delicate" approach in the context of a presidential election. But Vigano said the concerns were so worrisome that bishops had to act.

"It goes without saying that the Catholic Church in the United States is living in a particularly challenging period of its history," Vigano told an Atlanta meeting of the U.S. Conference of Catholic Bishops. "Of course, I am thinking of the whole question of freedom of religion and of conscience."

The bishops plan two weeks of rallies and prayer services on religious freedom leading up to July Fourth. Vigano called the religious freedom campaign "praiseworthy," saying, "It has my full support."

The national gathering is the bishops' first since dioceses filed a dozen lawsuits against an Obama administration mandate that most employers provide health insurance covering birth control. The rule generally exempts houses of worship, but faith-affiliated hospitals, charities and schools would have to comply.

Obama has offered to soften the rule for religious employers by requiring insurance companies to cover the cost instead of religious groups. The administration has been taking public comment while working out the details, but bishops have said that the changes proposed so far haven't gone far enough.

Many Catholics across the political spectrum have said they agree a broader religious exemption is needed for the mandate. But critics have said that the lawsuits appear politically partisan, especially during a presidential election.

"Most bishops don't want to be the Republican party at prayer, but their alarmist rhetoric and consistent antagonism toward the Obama administration often covey that impression," said John Gehring, of the liberal advocacy group Faith in Public Life.

The bishops have dismissed the suggestion of any partisan intent.

Bishop John Wester of Salt Lake City said the bishops were only responding to the federal policy announced in January.

"We need to be vigilant and we need to address these issues," Wester said. "The government cannot define religion for us."