National Electoral Council President Francisco Carrasquero made the announcement on Tuesday as anti-government demonstrators protested in the streets.
But opposition voters will have a chance to reconfirm disputed signatures, leaving open the possibility they could still meet the target to trigger a referendum, Carrasquero said.
The council's preliminary results showed the opposition had collected only between 1.7 million and 1.8 million valid pro-referendum signatures - short of the minimum 2.4 million required by the constitution.
"It's not enough," he told the BBC in Spanish before an expected official announcement.
He said an additional 600,000 to 700,000 signatures would be subject to reconfirmation.
Carrasquero spoke as troops and anti-government protesters skirmished in the streets for a fifth day.
National Guard soldiers fired tear gas to clear protesters in eastern Caracas, and demonstrators set up burning barricades to block several highways in the capital and other cities.
"These are not the correct figures"
A final decision on the referendum would be made in March after the complex reconfirmation process, which has been criticised by the opposition as a tactic to delay the vote.
Angry opposition leaders called the leak of the signature figures irresponsible and said they did not accept them.
"These are not the correct figures," said opposition leader Andres Velazquez, insisting they had handed in more than three million signatures in December.
Most of the capital of six million people remained generally quiet on Tuesday.
Smoke billowed from burning tires in the eastern Altamira district, where troops cleared charred debris and twisted metal from Monday night's street battle.
At least four people have been killed and dozens wounded in the latest violence to rattle the world's fifth largest oil exporter as Chavez opponents demanded the council allow them a chance to challenge a president they accuse of dictatorial rule.
Venezuela's oil operations - the nation's economic mainstay - have been unaffected by the protests, officials from the state oil firm PDVSA said.
But some traders fear a repeat of the two-month opposition strike at the start of last year that disrupted vital crude production.
Opposition leaders accuse pro-Chavez officials in the election council of trying to block the referendum bid by questioning thousands of signatures during the verification process.
They say they collected 3.4 million signatures.
The council, whose board is controlled by a 3-2 majority of pro-Chavez directors, was expected to send about one million signatures for further examination, a measure opposition leaders say will essentially scuttle the referendum.
Four people were killed in recent
Chavez, who survived a coup in 2002 and the grueling two-month strike last year, has dismissed the opposition petition as filled with forgeries.
He says his foes are fomenting violence in another attempt to topple him.
Military commanders say the armed forces will act to guarantee order and around 30 people have been arrested, including one opposition leader.
International observers, led by the Organization of American States, have struggled for more than a year to end the bitter political standoff.
After winning a landslide election in 1998, Chavez has battled growing opposition to his self-styled revolution, which promises to give the poor more benefits from Venezuela's huge oil wealth.
But his foes say he has failed to reverse years of neglect by previous governments.