Enthusiasm for President Barack Obama has abounded around his inauguration as many Americans anticipate a time of change. But now with a pro-choice president, tens of thousands of Christians and pro-life advocates are doubling their efforts hoping for a specific change – justice for the unborn.

"While millions are celebrating the Inauguration of President Obama, it is critical to be a voice and witness for those who have no voice," said the Rev. Patrick J. Mahoney, director of the Christian Defense Coalition. "That is the 53,000,000 innocent children that have been lost through abortion."

Mahoney and a group of pro-lifers stood along the Inaugural Parade route in Washington, D.C., on Tuesday holding pro-life banners.

It was just one of many pro-life events taking place that day in Washington and other cities, including Olympia, Wash. Pro-life advocates worry that Obama will push the Freedom of Choice Act, which could lead to more abortions.

The events lead up to the 36th anniversary of Roe v. Wade, the 1973 Supreme Court decision that legalized abortion, on Thursday.

Participants in the annual March for Life in Washington, D.C., on Thursday are hoping their message will resonate louder this year as they now march under the administration of Obama, who has been described as the most abortion-friendly president ever elected.

March for Life organizers have extended an invitation to Obama to speak at the rally on the National Mall.

"America needs your strong leadership as President of all of the people to stop the intentional killing of an estimated 3,000 preborn boys and girls each day and the brutalizing of mind, heart and body of pregnant mothers," the invitation addressed to Obama states. "This evil continues because some public officials and other citizens are indifferent to the fatal errors of Roe v. Wade and the critical need to overturn the illicit Roe v. Wade."

Catholic bishops also wrote a letter to Obama asking the president not to reverse the pro-life policies – including a ban on federal funding for embryonic stem cell research and protection of health care workers who object abortion due to moral or religious beliefs – that were put in place during the Bush administration.

Noting that Obama had at one occasion not been able to provide a definite answer to when a baby has human rights, Cardinal Francis George, who wrote the letter on behalf of the U.S. Conference of Catholic Bishops, stated: "Uncertainty as to when human rights begin provides no basis for compelling others to violate their conviction that these rights exist from the beginning. After all, those people may be right. And if the goal is to reduce abortions, that will not be achieved by involving the government in expanding and promoting abortions."

Last August, then Democratic nominee Obama told Pastor Rick Warren at a forum that it was above his pay grade to answer the question of when life begins. Obama later explained to ABC News that the question is "pretty tough" and he wanted to communicate that he doesn't "presume to be able to answer these kinds of theological questions."

Obama's answer to the life question did not please evangelicals. Then Republican nominee Sen. John McCain had gained the praise of evangelicals when he, without hesitation, replied that life begins at conception.

And while Obama has expressed his willingness to limit late-term abortions, as long as there is an exception if a woman's health is at risk, and talked of trying to reduce the need for abortions in the first place, evangelicals aren't satisfied with just reducing abortions. They want to end it.

Obama supporters who are Christian have been criticized by fellow believers for throwing their support behind a pro-choice candidate.

Bishop Donald Hilliard of Cathedral International, however, recently responded to such criticism by stating, "First of all, Barack Obama is pro-life, but he respects a woman's right to make a choice."

"I'm pro-life," Hilliard, who co-chaired the African American Church Inaugural Ball on Sunday, assured. "But when you put the two together, Obama and McCain, I believe that the more compassionate, the more caring, the more concerned candidate was Barack Obama. And he evidently was God's choice because he's in office."

Still, for many believers and pro-life advocates, their concerns for the unborn are great under the new administration.

Pro-life marches, rallies and prayers will be held across the country on Thursday. The push to end abortion will continue next month on Feb. 25 when pro-life advocates in 118 cities across 41 states and Canada pray and fast in a 40-day campaign.