BAGHDAD, Iraq -- The first criminal case has been filed against former President Saddam Hussein for his alleged role in a 1982 massacre of more than 150 people, and he may be tried as early as September, the chief investigative judge of Iraq's special tribunal announced yesterday.

The announcement came on a day when suicide bombers killed 22 people in the Baghdad area, as insurgents stepped up a relentless campaign that claimed more than 90 lives a night before in a bombing near a Shiite mosque south of the capital.

The trial of Saddam would come at a time when the Shiite-led government is trying to lure Sunnis away from the insurgency. Saddam, who was president of Iraq from 1979 until the U.S.-led invasion in 2003, has been in U.S. custody since he was captured in December of that year. The tribunal's investigators have sifted through evidence of his alleged involvement in about a dozen atrocities committed while he was in power.

The 1982 massacre in the Shiite Muslim village of Dujail was a relatively minor incident in Saddam's reign, compared with other massacres, such as a chemical weapons attack that killed an estimated 5,000 ethnic Kurds in the northern town of Halabja in 1988, and the brutal suppression of a revolt by Shiites after the 1991 Persian Gulf War.

But the limited scope of the Dujail massacre made it easier to investigate, producing a less complex case than other alleged crimes, sources close to the tribunal said.

Because the Iraqi justice system organizes trials around specific events rather than individuals, Saddam could be named as a defendant in subsequent cases. Or, if convicted in the Dujail case and sentenced to death, he could be executed before the other cases are brought to trial. Iraqi officials have said they are under heavy popular pressure to try and put Saddam to death swiftly. But they also say they are committed to ensuring that the former dictator is dealt with fairly.

Saddam is alleged to have ordered the killings in Dujail, about 50 miles north of Baghdad, in retaliation for an attempt on his life there on July 8, 1982. In an ambush organized by the Dawa party -- a Shiite political group whose members include Iraq's current prime minister, Ibrahim Jafari -- gunmen concealed in a palm grove fired on Saddam's passing motorcade. Within hours, army helicopters were conducting airstrikes on Dujail and soldiers were rounding up villagers. Hundreds were imprisoned, and many of them were tortured or executed.

Three men who allegedly orchestrated the massacre are Saddam's co-defendants in the case: his half brother and former intelligence chief, Barzan Tikriti; former Vice President Taha Yassin Ramadan; and Awad Haman Bander Sadun, the former chief judge of the Revolutionary Court that sentenced 143 men from Dujail to death.

Judge Raeed Juhi said the investigation into the massacre had been completed and that the special tribunal's investigative court had referred the case against Saddam to the tribunal's trial court. The move is roughly analogous to the issuing of an indictment in the United States, though the defendants will not be formally charged until they appear in trial court.

"By this announcement, the Special Tribunal has moved into the actual trial of the former regime figures," Juhi said.

Speaking to reporters on the anniversary of the coup that brought the Baath Party to power in 1968, Juhi said the tribunal's investigators are developing other cases that would involve several of Saddam's top lieutenants, including ex-vice president Tariq Aziz and Ali Hassan Majeed, also known as "Chemical Ali," who directed the operation that killed or displaced hundreds of thousands of Kurds in the late 1980s.

Under the statute that established the special tribunal, the trial cannot begin for at least 45 days. During that period, defense lawyers will be able to see the prosecution's case for the first time and can file motions that, according to sources close to the tribunal, could further delay the start of the trial.

A leading member of Iraq's National Assembly said Saddam's trial could not go forward until the assembly passed a law legitimizing the special tribunal, which was created in December 2003 by the U.S.-appointed Iraqi Governing Council.

"We in the National Assembly, which is the only legal, elected body in Iraq, believe that a new law should be passed to form this special tribunal," said Hussain Shahristani, deputy chairman of the assembly. Shahristani said such a law would be passed next week.

It was unclear whether any new legislation would affect the legal standing of work that the tribunal has already done. A tribunal spokesman declined to comment on the matter.

As for the insurgency, in the past week alone, at least 170 people were killed in suicide bomb attacks throughout Iraq.

Three U.S. soldiers were killed over the weekend, including one yesterday when a homemade bomb exploded in central Iraq, the military said. At least 1,766 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count.

Elsewhere, one car bomber yesterday struck the offices of Iraq's electoral commission in eastern Baghdad, killing five election employees and one policeman. The commission said in a statement that it "affirms its determination to continue the electoral process," including plans for a national referendum on a new constitution and balloting for a new government later this year.

In another suicide attack, insurgents dumped two bodies on the road, then struck police who stopped to inspect them, the U.S. military said. Two policemen and one civilian were killed in the explosion.

About an hour later a suicide car bomber attacked a police convoy near a bus station in southern Baghdad, killing three police commandos and four civilians, police Capt. Talib Thamir said.

Another suicide car bomber missed a U.S. convoy but blasted two minibuses, killing six civilians in Mahmoudiya, about 20 miles south of Baghdad, police Capt. Rashid al-Samarie said.

The Associated Press contributed to this report.