MONTCLAIR, N.J. - The biggest contrast in the first debate among the four Democrats running for the Senate came down not to policy, but approach.

Newark Mayor Cory Booker, the front-runner, said he has proven that he can cross the aisle to create progress in Newark and would bring a cooperative spirit lacking on Capitol Hill. But U.S. Rep. Frank Pallone said voters should place a premium on Washington experience.

U.S. Rep. Rush Holt touted his biography as a scientist, and Assembly Speaker Sheila Oliver called for adding a woman to New Jersey's all-male congressional delegation.

"It is time for new leadership in Washington that can bring people together," Booker said during Monday's televised debate at Montclair State University, recounting the theme he has stressed throughout his campaign.

He said he disagreed with Gov. Christie, a Republican, on most issues, but has worked with him because it was best for Newark.

Pallone had the sharpest retort.

"Being an experienced legislator does make a difference," he said, pointing to his work helping write President Obama's sweeping health-care overhaul. He called the controversial bill "one of the best pieces of legislation that we've ever passed."

For all of Booker's talk about Newark, Pallone, poised and detailed, said, "I don't think it's the same as having been in Congress and having worked with" lawmakers there.

And he attacked Booker's relationship with Christie.

"I don't think the governor has been a friend to cities at all," Pallone said after the debate.

Holt repeatedly stressed his background as a scientist who would "follow the evidence."

He began the day by launching a television ad saying Booker is "no progressive," and after the debate told reporters that he was "the one holding out a progressive position, unequivocal, clear."

Oliver said, "It is time to break up the old boys' network," noting that there are no women in New Jersey's delegation. In a dig at Booker's national reputation, she concluded, "This campaign is about New Jersey, no place else."

All reiterated themes they have sounded throughout the campaign.

Afterward, Holt, Pallone, and Oliver visited with reporters. Booker, off to another campaign event, sent a spokesman.

While Holt (directly) and Pallone (subtly) took aim at Booker in new campaign ads Monday, the mayor escaped the debate largely unscathed, leaving him as the heavy favorite to win the primary next Tuesday. Another debate is scheduled for Thursday.

Booker took large parts of his time to speak animatedly to the camera and tout his work in Newark.

The city's "immense progress," he said, is "a testimony to what people can do, taking on difficult challenges and working together."

He also made his first direct attacks on his opponents, saying Pallone and Holt both voted to allow school vouchers in the Washington school district even as they criticized him for supporting such programs in Newark.

Holt, stumbling at times, persistently pushed to the left, calling for a universal single-payer health care system, for example. Anything less, he said, amounted to caving to tea party opponents.

Pallone shot back, "Being an effective senator or congressman means you deal with what you can."

Oliver said she was "totally embracing" the Obamacare law because of its help for the uninsured.

On most issues, the Democrats were separated only by a matter of degrees - a key exception being vouchers, which Booker supported, calling them a lifeline for students stuck in struggling schools. The two congressmen warned that vouchers would drain funding for the public schools on which most students rely.

Pallone and Holt also called for the wealthy to pay more taxes to pay for more school funding and government investment in infrastructure projects, cities, and research.

The debate came as the campaigns began a final push on the airwaves.

Holt launched the most direct Democratic challenge to the mayor yet, airing a television ad criticizing Booker for not supporting a tax on carbon emissions, repealing the Patriot Act, or breaking up big banks.

The Booker campaign said the mayor has not taken a stand on carbon tax or breaking up banks - which the Holt team took as confirmation of its points.

In the debate, though, Booker pointed out that Holt had voted for the Patriot Act in 2001 but now wants to repeal it.

Changes to the law, Booker said, "need to be done in a sober manner." He said parts of the law are needed to fight terrorism.

Pallone began running a Spanish-language radio ad that tales aim at Booker's ties to New York's big financial firms.

"We need a senator who will stand with President Obama, not side with Wall Street," the ad says.

Much of the Monday night debate focused on foreign affairs: China, Syria, relations with Russia, and the controversial surveillance of Americans.

"The key right now is that we need aggressive oversight and action by Congress to do the right things and keep people safe," Booker said. Earlier, he said Washington was "not in balance" when it comes to weighing the two competing values.

Holt, a critic of surveillance on Americans, said, "the idea of vacuum cleaner, wholesale collection of information, personal information, about Americans is unacceptable."

Pallone said the balance had skewed "too much to surveillance."

Oliver, however, said that while there must be a balance, it is "imperative" for the president to "have the ability to protect us."

The winner of the primary will face either conservative leader Steve Lonegan or Central New Jersey physician Alieta Eck in the Oct. 16 general election.

Contact Jonathan Tamari at jtamari@phillynews.com or follow on Twitter @JonathanTamari. Read his blog, "Capitol Inq," at www.inquirer.com/CapitolInq.