A federal jury in Tampa, Fla., considering a wide array of criminal charges against a former college professor, Sami Al-Arian, and three co-defendants, returned verdicts yesterday against two of the men, but said it could not reach agreement on some charges against the other two defendants.

Judge James Moody placed the verdicts against the two defendants under seal, without describing the jury’s findings publicly or saying to which men the verdicts pertained. The judge then read the jury a standard instruction, known as an Allen charge, urging them to redouble their efforts to reach unanimous verdicts on the remaining charges.

The 51-count indictment in the case accuses Mr. Al-Arian, Sameeh Hammoudeh, Hatem Fariz, and Ghassan Ballut of Tinley Park, Ill., of being part of an American wing of a terrorist group active in Israel, Gaza, and the West Bank, Palestinian Islamic Jihad. The charges and weight of evidence against each defendant vary, but all of the men are accused of conspiracy to commit murder and to provide material support to a terrorist organization. All could face life in prison if convicted on the most serious charges.

The Tampa, Fla., jury, which began hearing evidence in the case in June, returned its partial verdicts just after 3 p.m. yesterday, according to court records. The six men and six women deliberated again briefly before quitting for the day. They are expected to return today for a 13th day of deliberations.

The trial is seen by some analysts as a significant test of the government’s ability to prosecute people alleged to have some ties to a terrorist group but who had no direct involvement in planning or carrying out terrorist acts. One of Mr. Al-Arian’s lawyers conceded in court that Mr.Al-Arian had “some affiliation” with Palestinian Islamic Jihad, but the remaining defendants insisted they had no connection to the group.