Families of more than 600 Sept. 11 victims filed a $3 trillion lawsuit Thursday, accusing Saudi princes, foreign banks, charities and the government of Sudan of funding the terrorist network that launched the attacks.

The lead plaintiffs are the widow, sister and parents of Thomas Burnett Jr., the San Ramon executive believed to have helped fight the hijackers of San Francisco-bound United Airlines Flight 93 and forced the jetliner down in rural Pennsylvania, short of its presumed target in Washington, D.C. All 44 people aboard were killed.

"It's up to us to bankrupt the terrorists and those who finance them so they will never again have the resources to commit such atrocities," Burnett's widow, Deena, said at a news conference in Washington, where the federal lawsuit was filed.

"As my son, Tom, told his wife, Deena, from the cabin of Flight 93, 'We're going to do something,' " said Thomas E. Burnett.

The suit alleges that Osama bin Laden's al Qaeda network was heavily financed by seven international banks and eight charitable foundations, with the active promotion and support of three members of the Saudi royal family. Bin Laden is a Saudi native, and 15 of the 19 hijackers were Saudi citizens.

The suit does not accuse any of the defendants of having a direct role in the Sept. 11 attacks, or knowing about them in advance, but says they knowingly funded terrorists and must be held responsible for the consequences.

"The charitable, financial, religious and political networks that front terror -- the defendant banks, charities, financial and business institutions - - are responsible for the deaths and injuries" of last September, the suit says.

LAWSUIT LOOKS TO LOCKERBIE

The lawsuit is partly modeled on the action filed against Libya in the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland. One lawyer in Thursday's case, Allen Gerson, helped negotiate a recent $2.7 billion settlement with the Libyan government on behalf of the families of the 270 victims.

Another precedent has resulted from a pending suit by the parents of an American-born teenager killed in a terrorist attack in Israel. The U.S. Court of Appeals in Chicago ruled recently the parents could sue Islamic charitable organizations that allegedly acted as fronts for the group blamed in the attack, Hamas.

Plaintiffs' attorneys in Thursday's suit said many of the defendants had considerable property in the United States from which damages could be collected. Some of the assets remain frozen, however, after the U.S. government declared several charities to be terrorist fronts.

The suit comes at a delicate time in U.S.-Saudi relations. In a briefing last month to a defense advisory board, a Rand analyst called Saudi Arabia an enemy of the United States. That assessment was quickly disavowed by the Saudi government and the Bush administration, both of which insisted that the two nations' ties were as strong as ever.

"We understand (the Bush administration's) concerns about the Saudis," said plaintiffs' lawyer Anne Kearse. "Our action is on behalf of our clients, to help with the war on terrorism."

The suit quoted the Rand briefing, belittled Saudi leaders' denials of connections to al Qaeda and stopped just short of accusing the Saudi government of complicity in the Sept. 11 attacks.

"Royal denials notwithstanding, Saudi money has for years been funneled to encourage radical anti-Americanism as well as to fund the al Qaeda terrorists, " the suit said. "Saudi Arabian money has financed terror while its citizens have promoted and executed it."

ROYAL DEFENDANTS

One Saudi prince named as a defendant, Sultan Bin Abdulaziz al Saud, has been the kingdom's defense minister since 1963. The suit quoted his denunciation of America's "Zionist and Jewish lobby" after Sept. 11 and said he had donated $6 million since 1994 to Islamic charities that finance al Qaeda, while also serving as the government's chief overseer of charitable fund raising.

Another royal defendant, Turki al-Faisal al Saud, was until a year ago the chief of the Saudi intelligence agency, which the suit described as "Osama bin Laden's nexus to the network of charities, foundations and other funding sources." The role of the third prince named in the suit, Mohammed al-Faisal al Saud, was not specified.

The suit did not name the Saudi government as a defendant but did target the government of Sudan, where two of the banks are based and where bin Laden had his headquarters from 1991 until he was expelled in 1996. Attorney Don Howarth explained that Sudan is on the U.S. State Department's list of sponsors of terrorism -- removing its immunity from terror-related damage suits -- but Saudi Arabia is not.

Attempts to reach the Saudi and Sudanese embassies in Washington for comment were unsuccessful.

The suit seeks $1 trillion on a variety of grounds for supporting or knowingly permitting terrorist activities. One claim seeks $3 trillion under a law providing triple damages for U.S. victims of international terrorism. In addition to compensation, the suit also seeks $100 trillion in punitive damages against Sudan.