More than 300 members of the Iraqi opposition gathered at a Times Square hotel tonight to rejuvenate their U.S.-backed campaign to overthrow Saddam Hussein, but last-minute cancellations punched holes in the opposition's newfound unity.

The National Assembly of the Iraqi National Congress, financed and promoted by the United States, is expected to select a new slate of leaders and is intended to foster unity after years of infighting.

Iraqi exile leaders, interviewed at their headquarters in the Liberty Suite of the Sheraton Hotel, conceded they have little chance of mounting a military challenge to the Iraqi president, despite a U.S. pledge last year of $97 million in surplus military equipment and training. Their real hope, they said, is that their display of unity will persuade Iraq's military to turn against its leader.

"We want to get rid of Saddam. And we have young Iraqis skilled in the arduous task of overthrowing Saddam Hussein," said Ahmed Chalabi, a London-based opposition leader. "But we are not here to fight the Iraqi army. We are here to attract the Iraqi army to our side."

While Congress has appropriated money to support the opposition, the Clinton administration has had difficulty finding ways to spend it productively. The Pentagon plans to give a 10-day training course to a handful of opposition members starting Monday at a base in Florida. But the course will focus on management skills and civics lessons and will not involve weapons or combat training.

Sen. Bob Kerrey (D-Neb.), Sen. Sam Brownback (R-Kan.) and David Scheffer, the U.S. ambassador at large for war crimes, pledged their support in an opening ceremony tonight.

"Containment has failed, and it's in our national interest to change our policy from containment to regime change," Kerry said in an interview. "We're not picking a leader. We're not picking a president. We're saying we will support you with such force as necessary for the liberation of Iraq."

Organizers portrayed the event as the first gathering since 1992 of opposition groups, including rival Kurdish factions, the umbrella Iraqi National Congress and the Constitutional Monarchist Movement, headed by a member of Iraq's former royal family.

But on the eve of the event, Hamid Al Bayati, a representative of a key Shiite group, the Tehran-based Supreme Council for Islamic Revolution in Iraq, decided not to attend. Massoud Barzani, president of the Kurdistan Democratic Congress, also declined to come, though he sent a large delegation to meet with his longtime rival, Jalal Talabani.

A few other Iraqi opposition organizations--such as the Iraqi Communist Party, the Islamic Al Dawa party and the Syrian Baath Party--also stayed away, said Mike Amitay, an analyst at the Washington Kurdish Institute.

Amitay said many of the invitees were afraid to be too closely associated with Washington. "They are reluctant to do anything to upset Saddam Hussein, because the U.S. has not given them ironclad assurances that [the United States] will prevent the Iraqi leader from moving against them," Amitay said.

The unusual venue, in the Broadway theater district, was not the opposition's first choice. As he distributed "Free Iraq" T-shirts, Chalabi said U.S. Secretary of State Madeleine K. Albright had vetoed a proposal to hold the event in northern Iraq because the United States could not guarantee the attendees' security. Instead, the State Department hired a public relations firm, Burson-Marsteller, and a Springfield contractor, Quality Support, to organize the event, Chalabi said.

Brownback called the meeting a "first step" toward ousting Saddam Hussein, but said he is not convinced that the Clinton administration is committed to completing the job. The White House is moving at a "snail's pace" and probably will just "hand it off to another administration," he said.

Washington's last effort to overthrow Saddam Hussein ended in disaster. In September 1996, the Iraqi military rolled into northern Iraq, crushing a CIA-sponsored insurgency and executing about 100 members of the Iraqi National Congress. "We were let down by the Americans," said Latif Rashid, a London-based representative of Talabani's Patriotic Union of Kurdistan.

Scott Ritter, a former U.N. arms inspector, said he was asked by a group of Republican senators to participate in the campaign to oust Saddam Hussein. But after meeting with Chalabi, he said, he came away convinced that the effort was not serious.

"Americans supporting this haven't a clue what's going on in Iraq. This is a political cause celebre that has no chance of succeeding," Ritter said.