BAGHDAD, Iraq -- The murder scene had the markings of a gangland slaying, but the motive was not money, revenge or a drug deal gone sour.

Hadi Saleh, a 56-year-old labor rights advocate and official of Iraq's Communist Party, affectionately known by friends as "Abu Furat," was found strangled in his home with a steel wire, his face beaten to a pulp, his hands bound behind his back.

Saleh's files, containing the names and addresses of colleagues in both the party and the labor federation he led, were stolen, his humble home ransacked.

The scene resembled the interrogation rooms of deposed President Saddam Hussein's security forces, whom officials suspect. Saleh may or may not have given them information; his files certainly did.

"The people who did this are very clearly members of the Baath Party from the former regime," said Mohammad Jassem Abad, a leader of the Communist Party, which is participating in the upcoming parliamentary elections that the insurgents violently oppose.

"The way they killed him makes it very clear they're the ones who did this," he said. "It is their methods. His assassination wasn't random. It was perfectly chosen."

Twenty months after the U.S. invasion of Iraq, the country's increasingly brutal insurgency remains a shadowy phenomenon. But its tactics and targeting are becoming more sophisticated and precise, leading many Iraqi and U.S. officials to believe that Saddam's old security apparatchiks have asserted control to settle old scores and destabilize the Jan. 30 elections.

"These people have blood on their hands and are murderers," said one high-level justice ministry official, who asked not to be named. "They want everyone hiding behind walls, so they can control the streets."

Most of the targets are Shiites and Kurds in the new Iraqi security forces or political leadership, including the Communists. Saddam drew his allies from among his fellow Sunnis, who know that the majority Shiites and the Kurds in northern Iraq will assume control of the national government if the elections come off in three weeks as planned.

After a brief respite following Ramadan and the U.S.-led assault on Fallujah in early November, the violence in Iraq has returned to fever pitch.

Last week, gunmen assassinated the governor of Baghdad in a professional hit that was filmed and posted on the Internet. They also killed the police chief of the capital's huge Shiite neighborhood of Sadr City.

In Mosul, the bodies of 18 young men from Baghdad believed killed last month were discovered, all shot in the head with their hands bound. In Basra, police turned up two charred, beheaded bodies in the office of election organizers. Suicide car bombers killed at least 100 members of the Iraqi security forces over the course of the week.

Insurgents issue no public statements, save for their spectacular acts of violence. They offer no political agenda, aside from driving U.S. troops out of the country.

Officials and analysts are left to divine their mix of motives and their manpower. Figures range wildly from 5,000 to 40,000 to 200,000 fighters and supporters. The Interior Ministry estimates the number of former hard-core Iraqi intelligence officials as no more than 10,000.

Even top U.S. military officials often sound bewildered by the insurgency.

"There are hard-core terrorists fighting for an ideology. There are young impoverished men looking to make some money," said Lt. Gen. Thomas Metz, commander of all forces in Iraq, at a recent news conference. "It would change by province. It changes by time of year. It changes by the illumination of the moon. It changes by the weather."

The bulk of Saddam's supporters came from Sunni Arab communities in Tikrit, Mosul and Fallujah. A majority of insurgents captured or killed have been Iraqi Sunnis -- up to 95 percent of those detained, wrote military expert Anthony Cordesman of the Center for Strategic International Studies in Washington, in a draft report dated Dec. 22.

The insurgents are an ideologically mixed lot, Cordesman and other experts say. Aside from Saddam's henchmen, they include Sunni nationalists enraged by the U.S. occupation and foreign Islamic extremists -- possibly followers of Osama bin Laden or Jordanian terror leader Abu Musab Zarqawi -- who would like to drive the United States out of all Muslim lands. Some appear to be career criminals or young men willing to kill for money.

They are organized into loose cells and keep electronic communication to minimum to avoid detection. And they follow traditional insurgent tactics, Cordesman wrote.

They attack the security forces, public officials and economic infrastructure to sap public confidence in their leaders. They attack the United Nations, embassies and aid organizations to drive out the international community.

They hope their acts of savagery provoke equally violent responses from occupation and interim government forces, which, in turn, would breed more insurgents and more anger toward the Americans. "The more horrifying the attack, or incident, the better," Cordesman wrote.

The insurgents' main weakness may be the diversity of their goals. All want the Americans out, but what would come afterward is unclear.

Some wish to establish an Islamic utopia modeled on the teachings of puritanical Salafi and Wahabbi strains of Sunni Islam. Others wish to reassert the secular supremacy of Iraq's Sunni Arab minority. Others may simply want anarchy to protect themselves from the wrath of those they tormented for decades.

If the insurgency has a brain, U.S. and Iraqi officials increasingly believe, it belongs to well-trained intelligence operatives of the Saddam regime, like the men believed to have tortured and killed Saleh, or the men who apparently tied up the 18 young men -- some as young as 14 -- and coldly executed them one by one.

"The violence is part of a big plan to end the democratic process and stop the elections so they can establish a new dictatorship like during Saddam Hussein's time," said Abad, of the Communist Party.

"Those criminals are wanted by the Iraqi justice system," he said. "They're very afraid that Iraq is going to have a justice system and they're going to have to stand before that justice system and be charged with killing all of our comrades."