A defense lawyer who won the partial acquittal of a Florida college professor accused of ties to Palestinian Islamic Jihad is taking on the case of a Palestinian Arab activist charged in Chicago with illegally aiding another terrorist group, Hamas.

The Washington-area attorney, William Moffitt, agreed last month to represent Abdelhaleem Ashqar, who is facing trial in October on charges of racketeering conspiracy, obstruction of justice, and contempt of court. An indictment returned in 2004 alleged that the Virginia resident “functioned as a conduit of money for Hamas members both in the United States and abroad.”

During a six-month federal trial in Tampa last year, Mr. Moffitt led the defense of a former University of South Florida computer science professor, Sami Al-Arian. A jury acquitted Al-Arian on eight charges and deadlocked on nine others.

Al-Arian ultimately pleaded guilty to one count of providing services to a designated terrorist group and agreed to be deported. A judge imposed about a year of additional jail time on the former academic, who has been in custody since his arrest in 2003.

The outcome at trial, which came after more than a decade of investigation of Al-Arian by federal authorities, was widely viewed as an embarrassment for the government and a victory for Al Arian and Mr. Moffitt.

“That’s obviously why Dr. Ashqar was interested in hiring him,” a Chicago law professor who will serve as co-counsel to Mr. Moffitt, Andrea Lyon, said in an interview yesterday. “Bill is one of the most prominent defense lawyers in the country and he’s been successful against the government, which is not easy to do because the government has unlimited resources.”

Reached at his Virginia home yesterday, Mr. Moffitt declined to say whether the Al-Arian case influenced Mr. Ashqar’s decision to hire him. “I’m not at liberty to discuss all of that,” he said.

Mr. Moffitt acknowledged a penchant for the complicated, terrorism-related trials. “Amongst criminal law cases, you have to say these are the most interesting cases,” he said. “They get you into the biggest fights with the government.”

Asked if he was developing a reputation as the lawyer of choice for those accused of abetting terrorism, Mr. Moffitt pointed to his other successes. “I also just did the Cynthia McKinney case,” he said, referring to his work for a Georgia congresswoman whom a grand jury recently decided not to prosecute for an alleged assault on a Capitol Police officer. “I hope I’m not typecast as a lawyer for congress people, either,” Mr. Moffitt quipped.

There are many parallels between the Tampa case, which targeted the alleged leadership in America of Palestinian Islamic Jihad, and the Chicago case, which targets those in America allegedly affiliated with Hamas. Testimony at Al-Arian’s trial portrayed the two extremist groups as rivals for the sympathies and financial support of Palestinian Arabs worldwide.

The Florida charges rested primarily on evidence from the 1990s, some of which jurors found less than urgent by 2005. The indictment in the Illinois case is also based almost exclusively on alleged money transfers and meetings from the 1990s.

Both cases also involve troubling facts that could make federal authorities look less than competent. The Tampa case named as a co-defendant Al-Arian’s brother-in-law, Mazen Al-Najjar, although he was deported from America in 2002, just months before the indictment was returned. The Chicago case names as a co-defendant a Hamas leader who was deported from America in 1997, Mousa Abu Marzook.

Messrs. Al-Najjar and Abu Marzook are now considered fugitives by the country that deported them.

Prosecutors in the Chicago also case face one complication not present in Al-Arian’s trial, the emergence of Hamas as the elected government of the Palestinian Authority. While America and Israel have refused to deal with Hamas, defense lawyers may be able to use the election outcome and the recognition of Hamas by other countries to portray the group as part of the mainstream.

Mr. Moffitt, 57, can be an imposing, even combative, presence in the courtroom. During the Al-Arian trial, the defense lawyer repeatedly denounced the prosecution’s tactics as a political attack on freedom of speech. According to local news reports in Tampa, he had an in-courtroom confrontation with a prosecutor and quarreled with his client, Al-Arian, who wanted to testify in his defense. In the end, Al-Arian called no witnesses.

During the trial, Mr. Moffitt was scolded by the judge for nodding off from time to time. The lawyer, who recently had both his knees replaced, blamed exhaustion due in part to knee and kidney ailments. “I’m undergoing rehabilitation,” he said yesterday. “I’m doing fine.”

The Al-Arian case may also have had a professional impact on Mr. Moffitt, a graduate of American University’s Washington College of Law and past president of the National Association of Criminal Defense Lawyers. He recently split with the Philadelphia-based law firm he joined in 2004, Cozen O’Connor. “Cozen and I have settled whatever I’m going with,” he said, without elaborating.

In Mr. Ashqar, Mr. Moffitt has found another strong-willed and lively client. In 1998 and again in 2003, Mr. Ashqar was jailed for refusing to testify before federal grand juries investigating terrorism financing in America. As part of his defiance, he reportedly undertook a six-month hunger strike.

Last year, Mr. Ashqar ran unsuccessfully for president of the Palestinian Authority, even though he was under pre-trial house arrest in Virginia. He has pleaded not guilty and denied being a member of Hamas. However, Mr. Ashqar is adamant that he will not inform on other Palestinian Arabs.

“I’d rather die than testify,” he has declared, according to a Web site collecting funds for his defense, www.free-ashqar.org.