Will there be anything left of Obama by the time they’re through?

Are the American people ready for an elected president who was educated in a Madrassa as a young boy and has not been forthcoming about his Muslim heritage?

This is the question Sen. Hillary Rodham Clinton’s camp is asking about Sen. Barack Obama.

An investigation of Mr. Obama by political opponents within the Democratic Party has discovered that Mr. Obama was raised as a Muslim by his stepfather in Indonesia. Sources close to the background check, which has not yet been released, said Mr. Obama, 45, spent at least four years in a so-called Madrassa, or Muslim seminary, in Indonesia.

“He was a Muslim, but he concealed it,” the source said. “His opponents within the Democrats hope this will become a major issue in the campaign.”

Sources said the background check, conducted by researchers connected to Senator Clinton, disclosed details of Mr. Obama’s Muslim past. The sources said the Clinton camp concluded the Illinois Democrat concealed his prior Muslim faith and education.

“The background investigation will provide major ammunition to his opponents,” the source said. “The idea is to show Obama as deceptive.”

In two best-selling autobiographies “The Audacity of Hope: Thoughts on Reclaiming the American Dream” and “Dreams from My Father: A Story of Race and Inheritance” Mr. Obama, born in Honolulu where his parents met, mentions but does not expand on his Muslim background, alluding only to his attendance at a “predominantly Muslim school.”

[Sources] said the background check concerned Mr. Obama’s years in Jakarta. In Indonesia, the young Obama was enrolled in a Madrassa and was raised and educated as a Muslim. Although Indonesia is regarded as a moderate Muslim state, the U.S. intelligence community has determined that today most of these schools are financed by the Saudi Arabian government and they teach a Wahhabi doctrine that denies the rights of non-Muslims.

Although the background check has not confirmed that the specific Madrassa Mr. Obama attended was espousing Wahhabism, the sources said his Democratic opponents believe this to be the case and are seeking to prove it. The sources said the opponents are searching for evidence that Mr. Obama is still a Muslim or has ties to Islam.

Mr. Obama attends services at Trinity United Church of Christ in Chicago’s South Side. However, he is not known to be a regular parishioner.

“Obama’s education began a life-long relationship with Islam as a faith and Muslims as a community,” the source said. “This has been a relationship that contains numerous question marks.”

The sources said Mr. Obama spent at least four years in a Muslim school in Indonesia. They said when Mr. Obama was 10, his mother and her second husband separated. She and her son returned to Hawaii.

Ms. Clinton regards Mr. Obama as her most formidable opponent and the biggest obstacle to the Democratic Party’s 2008 presidential nomination. They said Ms. Clinton has been angered by Mr. Obama’s efforts to tap her supporters for donations.

In late 2006, when the Illinois senator demonstrated his intention to run for president, the Clinton campaign ordered a background check on Mr. Obama, the sources said. Earlier this week, Mr. Obama established an exploratory committee, the first step toward a formal race.