WASHINGTON -- The Bush administration is laying the groundwork for prosecuting Iraqi leader Saddam Hussein and a "dirty dozen" other officials for genocide, "ethnic cleansing," mass executions, rape and other crimes against humanity.

The push to prepare dossiers for war crimes prosecutions, which now involves the State Department, the Pentagon and the intelligence community, reflects the growing momentum in Washington toward ousting Hussein and the increasing preparation for the days afterward -- even though President Bush has not yet made a decision on going to war against Iraq.

"We need to do our part to document the abuses, to collect the evidence that points to who is responsible," said Pierre-Richard Prosper, the State Department's ambassador at large for war crimes and a former U.N. war crimes prosecutor for the Rwanda tribunal. "We feel there has to be accountability for what has occurred. You can't brush aside the deaths of more than 100,000 people."

In a telling reflection of how the Iraqi leader relies on family and tribe to enforce his rule, half of the dozen on the U.S. list are members of Hussein's family: two sons, three half brothers and a cousin.

After Hussein, the next name on the list is Ali Hassan Majid, nicknamed "Chemical Ali" for his role in a 1988 operation--code-named Al Anfal, or "the spoils"--that used chemical weapons to kill tens of thousands of Kurds in northern Iraq.

Majid, a cousin of the Iraqi president, was also responsible for putting down 1991 uprisings by northern Kurds and southern Shiites after the first Bush administration called for Iraqis to oust Hussein.

At least 130,000 civilians have been killed as a result of deliberate regime policies during Hussein's 23-year rule, although that might prove to be only a fraction of the final tally, according to U.S. officials and human rights groups. Tens of thousands, including women, children and the elderly, were victims of chemical weapons attacks.

In a massive ethnic cleansing campaign, more than 120,000 Iraqis--primarily Kurds, Turkomans and Assyrians, none of whom are Arabs--have been forcibly expelled from the area around the northern city of Kirkuk to "Arabize" the oil-rich region, government and private groups say.

In the northern region known as Kurdistan, ethnic cleansing that began in 1991 has accelerated in recent months, according to Human Rights Watch. Every week, anywhere from three to 20 families are forcibly expelled from their homes and towns, said Hania Mufti, an Iraq specialist with Human Rights Watch who just returned from a fact-finding mission to the region.

The issue of justice is also key to Iraqis, both for healing deep wounds and for rebuilding the nation.

"For Iraqis and the international community, the issue of addressing Saddam's crimes against humanity is as important as addressing his possession and use of weapons of mass destruction," said Sermid Sarraf, an Iraqi American lawyer based in Los Angeles who works with the State Department on government transition issues.

The United States, with varying degrees of support from Iraqi opposition groups and human rights organizations, is looking at a three-tiered system of tribunals to deal with the thousands of army commanders, ruling Baath party officials, government employees, and security and intelligence agents implicated in war crimes.

In a break with the recent pattern of international war crimes prosecutions for the former Yugoslavia and Rwanda, the administration now favors a tribunal to try top officials inside a "free Iraq," with Iraqi and foreign judges, probably including Americans, according to administration officials.

The tribunal would prosecute the leadership--which could well expand beyond the original 12 after further investigations--for violations of both Iraqi law and international conventions.

"If and when there is a regime change, the appropriate forum should be at home, in a free and democratic Iraq," said Prosper, a former deputy district attorney in Los Angeles who dealt with hard-core gangs.

The concept has been endorsed by the Iraqi Jurists Assn., an exile group based in London, and by more than 40 Iraqi emigre judges, law professors and legal experts who met last month in Italy to discuss a transitional justice system in the event of Hussein's ouster.

The hybrid is also a model necessitated by the Bush administration's opposition to the International Criminal Court, human rights groups say. Washington would look hypocritical if it asked for a United Nations-mandated war crimes tribunal now.

"Other nations would see the U.S. action on Iraq to be particularly self-serving in the absence of cooperation on an international criminal court, which the rest of the world is keen on," said Michael Amitay, director of the research group Washington Kurdish Institute.

A similar hybrid of local and foreign judges and lawyers is being used to deal with war crimes trials stemming from the decade-long civil conflict in the West African nation of Sierra Leone, although human rights experts are concerned about the precedent this model would establish if used in Iraq.

"It's a practical approach, but the international community would like to see these people dealt with in a way that conforms with the developing law on crimes against humanity, especially given that these crimes are so much more severe than anything dealt with anywhere recently," said Charles Forest, chief executive of Indict, an international group based in London that is amassing information on Iraqi war crimes.

After the trials of the top leaders, the next level--potentially dealing with hundreds or even thousands of offenses, because the war crimes go back a full generation--would be left to local courts, U.S. officials say.

"The pattern globally is that midlevel cases can be dealt with by a conventional domestic system which is accepted and known by the people. It also serves as an important means of reviving the justice system," said an administration official who requested anonymity.

The third and largest group of cases might never go to trial but would instead be worked out through a group similar to the Truth and Justice Commission in South Africa that would grant a form of amnesty in exchange for a full accounting of crimes committed.

"One thing we have learned with war crimes around the world is that it's impossible to prosecute each and every perpetrator, as the number is so large," Prosper said. "You have to deal with the leaders to send a strong signal that justice will prevail. But the treatment of the balance of cases is more flexible, depending on the needs of society."

To avoid violent retribution after regime change in Baghdad, the exile group of jurists has issued a communique calling on fellow Iraqis not to take the law into their own hands.

"There are millions of Baath party members who joined the party mainly to advance their jobs or survive but aren't guilty of crimes," said Sarraf, who attended the meeting last month in Italy. "Then there's the guy in the army who killed someone on orders and to stay alive. Those individuals who can raise defenses such as 'involuntarily killed on threat of losing their own lives' ought to be allowed to use that as a defense."

The decision to prepare for war crimes prosecutions follows 11 years of inaction on Iraqi war crimes despite a wealth of data, eyewitness accounts and more than 18 tons of seized Iraqi documents, according to the Iraqi opposition and human rights groups.

Ironically, the first Bush administration opted not to push for such prosecutions even after the 1991 uprisings, which were called for personally by President George H.W. Bush.

The Clinton administration also did not push the U.N. Security Council for either a tribunal or a "commission of experts" on Iraqi war crimes, and that resulted in missed opportunities to put pressure on Hussein's regime, according to Iraqi and human rights groups.

"Over the years, the U.S. has failed to take a leadership role in bringing this regime to justice, which could have been done without toppling it. The U.S. could have pushed for an apparatus that would demonstrate the regime's criminality and further isolate it by obligating other countries to arrest and extradite any Iraqi official who left Iraq," Amitay said.

"We might not be where we are today if there had been action."