A former college professor on trial in Florida for leading the American wing of a terrorist group, Palestinian Islamic Jihad, yesterday passed up an opportunity to take the witness stand or present other evidence to rebut the five-month-long case put on by federal prosecutors.

Since June, a federal judge and jury in Tampa has heard dozens of law enforcement agents and government witnesses testify about the alleged involvement of the former academic, Sami Al-Arian, and three co-defendants with the Syria-based terror organization, which has killed dozens and wounded hundreds in suicide bomb attacks in Israel and the West Bank. The charges in the case include conspiracy to commit murder, extortion, and providing material support to a terrorist organization.

After the government rested its case yesterday, Mr. Al-Arian’s attorney, William Moffitt, rose and denounced the prosecution as an “all-out assault on the First Amendment.” Then, in a move that startled some courthouse observers, Mr. Moffitt announced that Mr. Al-Arian would not present a defense. Another defendant, Sameeh Hammoudeh, then began presenting his defense. Two other defendants, Ghassan Ballut and Hatem Fariz, are expected to follow.

“The government has not proven Dr. Al-Arian has done anything but speak,” Mr. Moffitt told reporters at the courthouse, according to the Associated Press. Mr. Al-Arian’s decision to forgo a defense followed an in-court dispute Wednesday between the defendant and his attorney that became so heated that Judge James Moody Jr. suspended the trial. Lawyers from another firm met with Messrs. Al-Arian and Moffitt in an apparent effort to sort out the disagreement.

A lawyer for Mr. Hammoudeh, Stephen Crawford, said he believed that the dispute related to whether Mr. Al-Arian should testify in his own defense. “Sometimes the client wants to take the witness stand. Sometimes it is best for them not to,” Mr.Crawford said.

Jurors have already heard a series of inflammatory statements from Mr. Al-Arian, including his cry of “Death to Israel!” at a 1988 conference. If Mr.Al-Arian took the stand, Mr. Crawford said, prosecutors could have questioned him about all of his prior comments. “The first thing I’d do as a prosecutor is take out that tape chanting ‘Death to Israel,’ play that five different times, in different ways, and ask him to explain it,” the defense lawyer said.

A former prosecutor who worked on the trial of suspects in the 1993 bombing of the World Trade Center, Andrew McCarthy, described as “smart” the decision to keep Mr. Al-Arian off the witness stand.

“The conviction road is littered with the carcasses of people who thought it was a good idea to get on the witness stand and got made mincemeat out of,” Mr. McCarthy said. “Sami is an educated, articulate guy. He’s wily. He’s got through his whole life being able to talk his way into and out of things. He probably figures he’s parried with tougher people than federal prosecutors before.”

Before his arrest in 2003, Mr. Al-Arian managed to ingratiate himself with high-ranking figures in American politics. He was pivotal in a Republican effort to win support from Arab-Americans in the 2000 presidential race. In March of that year, Mr. Al-Arian and his family were photographed with the future president, George W. Bush, and his wife, Laura, at a campaign event in Florida.

While Mr. Al-Arian is not presenting a defense, his attorney offered the photo as an exhibit during testimony earlier in the trial, according to Mr. Crawford. That means Mr. Moffitt will be able to use the image in closing arguments, which could take place as soon as next week, to suggest that the Palestinian-American activist could not have been much of a threat.

“It’s a legitimate point,” Mr.McCarthy said. The former prosecutor faulted politicians for courting Arab-American activists like Mr. Al-Arian, who had a publicly known record of inflammatory rhetoric. Still, Mr. McCarthy said, “It doesn’t make him not guilty.”

Another difficulty for the prosecution is that the evidence has not borne out suggestions that Mr. Al-Arian and his colleagues were fundraising for terrorist operations in the Middle East. In fact, testimony and bank records have shown that the think tank and other entities operated in America by the former University of South Florida professor drained money from Palestinian Islamic Jihad coffers in Syria and Iran.

Prosecutors have alleged that Mr. Al-Arian and others made relatively small payments to the families of suicide bombers, but defense lawyers said those gifts were simple charity.