* Opposition leader says he will not take part in a "joke" audit
* Maduro won April 14 election by narrow margin
By Daniel Wallis and Diego Ore
CARACAS, April 25 (Reuters) - Venezuelan opposition leader Henrique Capriles said on Thursday he will challenge President Nicolas Maduro's narrow election victory in the courts and that an audit of the vote being prepared by electoral authorities risked being "a joke."
Maduro, the hand-picked successor of late socialist leader Hugo Chavez, won the April 14 vote by less than 2 percentage points. The opposition says there were thousands of irregularities in the election and that their figures show Capriles won.
Both sides had agreed to an expanded audit of votes by the National Electoral Council. Since then Maduro has been sworn in as president and the opposition has grown increasingly frustrated by what it sees as foot-dragging by officials.
Capriles has insisted that the audit process be rigorous and include all relevant paperwork from polling centers.
"If we don't have access to those notebooks, we're not going to take part in an audit that would be a joke on Venezuelans and a joke on the world," he told a local TV station.
"The next step will be to challenge the election, which must take place in the next few days. With all the proof, all the elements we now have, we are going to challenge the election."
The election council has not responded to a demand by Capriles that it give concrete details of the audit by Thursday. It has stressed, however, that the process will only check that the system worked properly and the election results are "irreversible".
Capriles conceded that his legal challenge, which could in theory result in all or parts of the ballot being rerun, faced a tough path through Venezuela's courts.
Critics say Chavez packed the judiciary with loyal appointees during his 14 years in power.
"We're not going to challenge the election with the expectation that the Supreme Court is going to give us a favorable reply, or that the justice system will work," Capriles said. "But we're going to go through all the legal procedures."
MARCHES ON MAY 1
Both sides have called on their followers to march again on May 1, creating another potential flashpoint in the OPEC nation of 29 million people.
Capriles, a 40-year-old state governor who favors Brazil-style, business-friendly policies with strong social protections, confounded opinion polls to run a close finish against Maduro in the election, held just five weeks after Chavez's death from cancer.
The government calls Capriles a "fascist murderer" and blames him for post-election violence that it says killed nine people. This week, the "Chavista"-dominated Congress began an investigation of Capriles in connection with the unrest.
The government says the violence was proof that the opposition had tried to launch a coup, while the opposition accuses the authorities of exaggerating the unrest and including victims of common crime to boost its figures.
On Wednesday night, a televised news conference by the opposition leader was interrupted by a government "cadena" broadcast - which all local channels are required to show live - that held him responsible for the violence.
On Thursday, moments before Capriles was to be interviewed live on local station Globovision, another "cadena" began that lasted almost an hour and showed Maduro and his cabinet meeting business leaders in the western state of Zulia.
Again, the compulsory broadcast triggered noisy protests in wealthier Caracas neighborhoods where opposition supporters banged pots and pans in a traditional form of demonstration.
"It's just like last night," Capriles said later. "In everything he does, Nicolas keeps showing that he's scared. He doesn't want the people to know what's going on." (Editing by Christopher Wilson)