A federal judge on Thursday refused to block a summer reading program for incoming freshmen at the University of North Carolina who were told to read a book on the Quran, Islam's holy text.

U.S. District Judge Carlton Tilley rejected a request for a temporary restraining order from two taxpayers -- one an official of the conservative Family Policy Network -- and three unidentified freshmen.

The plaintiffs sued last month, seeking to overturn an assignment that 4,200 transfer students and freshmen at the Chapel Hill campus read and discuss Approaching the Qur'an: The Early Revelations by Michael Sells.

School officials said they assigned the book to help students understand Islam after the Sept. 11 attacks. The 19 hijackers, all Middle Eastern men, have been identified as followers of a radical brand of Islam.

The ruling means discussion groups scheduled for Monday can continue, unless the plaintiffs succeed with an appeal immediately filed in federal court.

The 180 discussion groups, meant to last about two hours, were to be led by volunteers from the faculty and staff. Students who objected to the assignment were allowed to explain their case and skip the discussion.

Tilley said students are not required to attend and are not graded on the sessions.

"This is not a religious activity," he said. "People do not have to participate."

The Virginia-based Family Policy Network maintained that a postcard sent to new students and information on the university's Web site indicated the assignment wasn't optional.

"The university initially required everyone to read the book and write a paper," said James Yacovelli, the center's state director and one of the plaintiffs. "Now you don't have to do anything."

But Celia Lata, the assistant attorney general representing the university, told Tilley the four-year-old reading program has never been mandatory.

"Learning in a university setting involves the ability to confront other viewpoints. That's the test," she argued. "A university that exposes students only to what they already know or believe would not equip them to live in the world."

Opponents said UNC denied students their religious freedom and was trying to indoctrinate them with a book that discussed only the most peaceful passages of the Quran.

Detractors say the 220-page book could convert Americans to the religion of terrorists blamed for the deaths of 3,000 people on Sept. 11.

The book contains commentary on 35 verses of the Quran and has a companion CD with audio recitations of several verses in different styles.

Carl Ernst, a professor of Islam at UNC, recommended it to the selection committee to help students struggling to understand Islam, a religion shared by 1.2 billion people.

Sells estimates 70 colleges have used his book, but it stirred little mainstream discussion until its selection by UNC.

The reading requirement met political pressure in the state House, which passed a budget proposal this week that would cut public money for UNC's reading program unless it gives equal time to all religions.

The stance was largely symbolic since the program costs relatively little and the General Assembly is weeks away from passing a final budget. The measure is not included in the Senate's budget proposal.