In a high-stakes two-hour live television appearance aimed at jumpstarting the flailing 'yes' campaign in France ahead of a May 29 referendum, Chirac also insisted the treaty could not be renegotiated if the 'no' camp were to prevail.
But the French president -- who has staked his prestige on approval of the constitution -- said he would not resign should voters reject the landmark text.
"France would cease to exist"
"Today, our political power alone, within Europe, allows us to defend our interests. If tomorrow we were to vote no, we would no longer have any power," Chirac told a group of 80 young adults picked by the Sofres polling institute.
"The reality is that you would have 24 countries that voted yes and then the black sheep that blocked everything", he said.
"France would be considerably weakened," he warned, adding that within Europe, "France would cease to exist politically."
Chirac also cautioned that "European construction would stop," adding: "The argument that we could renegotiate (the treaty) is not a serious one."
"Let's not be afraid," he urged the audience.
Treaty in jeopardy
The constitution, which aims to streamline decision-making in the expanded 25-member European Union, must be ratified by all member states. A rejection in France, one of the EU's largest countries, would effectively kill the treaty.
Since mid-March, more than a dozen opinion polls have indicated that French voters will reject the constitution in May. The most recent survey, published Thursday, put support for the 'no' camp at 55 percent.
Chirac argued that the constitution was necessary to create a "strong and organized" EU which could act as a counterweight to established powers like the United States and emerging states like China, India and Russia.
"You need rules to be organized. These rules are in the constitution," he said.
A tool of protest?
The French president also implored voters not to turn the referendum into a protest vote against the center-right government's gradual economic reforms, stubborn unemployment and decreasing purchasing power.
"Domestic policy has its own rules, rhythms and demands," he said. "At the moment when we are about to make a fundamental decision for the future of our country, for the future of Europe... I don't want that to be mixed up with the day-to-day politics of a European
country," Chirac said.
On the issue of Turkey's bid to join the EU, cited in some opinion polls as a reason for French opposition to the constitution, Chirac said the two ideas should not be mixed up, as Turkey's possible entry was "10, 15, 20 years" off.
"Wanting to confuse this issue with the constitution is absolutely either in bad faith or due to rather lightweight reasoning," the French leader added, while encouraging Turkey to pursue democratic reforms.
Preferential treatment for 'yes' campaign
Meanwhile, organizers said some 6000 people attended a 'no' rally at a central Paris theater, taking aim at Chirac and other supporters of the European constitution.
French anti-globalization activist Jose Bove criticized Chirac's television appearance as a "media-friendly show with TV presenters, without any real debate."
Those in the 'no' camp had also complained that Chirac did not face a political adversary on Thursday's broadcast, claiming the 'yes' campaign was getting preferential treatment in prime-time viewing hours.
Chirac's Union for a Popular Movement (UMP) supports the constitution, as does its ally in government, the Union for French Democracy (UDF).
The opposition Socialists are officially campaigning for the treaty but riven by an internal split on the issue. The Greens support the text.
The only parliamentary group that rejects the constitution is the Communist party.