CARACAS - Venezuelan President Hugo Chavez acknowledged Monday his first-ever election defeat after voters rejected reforms in a weekend referendum that would have strengthened his grip on power and turned his oil-rich country into a socialist state.

"Don't feel sad," a chastened-looking Chavez told his supporters via a media conference. He stressed that he had lost by only a "minimal" margin and was encouraged by the support he did get.

The National Electoral Council said "no" votes against the reforms had outweighed "yes" votes by a very narrow 51 to 49 percent.

"I tell you from the heart: For a few hours I debated with myself, in a dilemma," Chavez said. "I've now left the dilemma behind and I'm calm. I hope the Venezuelans are as well."

He added: "Now, Venezuelans, let's put our trust in our institutions."

Opposition members and sympathizers immediately celebrated their victory, setting off fireworks in Caracas and filling the streets with cheers and whistles.

Chavez supporters, in contrast, looked despondent in their red campaign colors, their "yes" flags and banners lowered.

It was the first time since Chavez came to power in 1999 that he has lost at the polls. In all his past elections, the charismatic leftwing firebrand triumphed with comfortable leads.

During his campaigning for the referendum, the president had labeled as "traitors" those swelling the ranks of the opposition -- including an unprecedented number of the country's poor, who, while still expressing affection for him, balked at endorsing his reforms.

Chavez, a firebrand critic of the United States with ties to Iran and Cuba, had been counting on the referendum to continue his rule beyond January 2013, when he must step down under the current constitutional two-term limit.

The 53-year-old former paratrooper had said he wanted the constitution overhauled so he could seek re-election "until 2050" -- when he would be 95.

He had also wanted to gain even tighter control over the country by putting more of the military under his command, permitting media censorship in times of emergency and scrapping the central bank's autonomy.

But street protests started by university students put paid to those ambitions, growing into the grassroots opposition movement that eventually vanquished him at the polls.

His exhortations that a "no" vote would be a vote for US President George W. Bush and US "imperialism" failed to carry the day in his favor.

There was a disturbing few hours after the vote, however, during which the government gave no results whatsoever and Chavez pondered what to do.

With the opposition clamoring for the release of figures -- and soldiers moving in to block entry to the National Electoral Council building -- a media conference was finally held in the early hours of Monday in which NEC chief Tibisay Lucena announced the defeat of the reforms.

Chavez mocked the opposition in his concession speech, saying that their concerns that he might refuse to accept the result were clearly misplaced.

"Now the tensions have dropped I hope they will see things more calmly," he said.

Fears remained of street violence in the wake of the result, however.

Chavez also warned right up to the eve of the referendum that he suspected the United States had a plan to exploit the vote to sow unrest, and he vowed to cut oil supplies to the US if he saw any meddling.

A historian, Margarita Lopez Maya, told AFP that the result was "a personal rout for the president" but overall good for the country.

"Chavez will survive, but will be forced to rethink the timing of his project and the ways he might be able to persuade the population," she said.

Venezuela's constitution prevents Chavez from re-presenting his constitutional reform under the current congress -- though he could conceivably appoint a constituent assembly to draft an entirely new basic law for adoption.
© 2007 Agence France Presse