Des Moines, Iowa ? Democratic presidential rivals united Saturday in attacking President Bush on national security, an issue on which voters rate him highly.

White House hopefuls, at a forum designed to highlight their differences, accused Bush of scrimping on domestic defense in favor of cutting taxes for the rich.

The 2004 contenders said the inability to ascertain the fate of suspected Sept. 11 mastermind Osama bin Laden was symbolic of what they contended was Bush’s failed policy on fighting terrorism.

The Democrats at the meeting, sponsored by the American Federation of State, County and Municipal Employees, said Bush talked tough on homeland security but did not deliver, and they said he used the issue largely to advance a right-wing agenda.

Taking on Bush’s homeland security policies marked a shift in emphasis for the Democrats, who were split on whether to go to war in Iraq. But bombings last week in Saudi Arabia and Morocco have raised questions about how effectively the administration has defused terrorist threats.

In response to a question from a New York City firefighter, Rep. Dick Gephardt of Missouri said the administration’s actions since Sept. 11, 2001, underscored his point about failings in homeland security.

Rescuers who went into New York’s World Trade Center “were union members, and they were heroes. They were patriots, and they did everything we asked them to do,” Gephardt said. Yet “when it came to passing a homeland security bill, this administration insisted on a bill that would take away the rights to organize.”

Workers in the Transportation Safety Administration, created in that legislation, cannot join unions for collective bargaining.

Al Sharpton cited the uncertainty about bin Laden. “Mr. Bush, the question you have not answered is, ‘Where is bin Laden?”‘ Sharpton said. “We need to go after those who went after us.”

Connecticut Sen. Joe Lieberman, an observant Jew who does not campaign on Saturdays, videotaped an interview with Gerald McEntee, president of the government workers’ union. It was shown at the meeting.

Sen. John Kerry of Massachusetts, who was in Iowa on Friday to lay out his health care plan, spoke to participants by telephone from New Hampshire, the first primary state.