By Andrew Cawthorne

CARACAS (Reuters) - President Nicolas Maduro said on Thursday punitive electricity rationing would be imposed on 15 shopping malls and drought-hit Venezuela's time zone would also be modified to save power.

Many of the South American OPEC nation's 29 million people are suffering daily, unscheduled water and electricity cuts as levels recede at the Guri dam complex providing nearly two-thirds of power needs.

Maduro, 53, whose popularity has suffered amid a national economic crisis and stuttering public services, said some major shopping centers had failed to supply their own generators despite being told to do so five years ago.

"The time has come to take a drastic rationing measure against a group of about 15 malls who did not obey the law and are consuming without conscience at a critical moment due to the 'El Nino' phenomenon," he said, without giving further details.

The socialist government says the El Nino weather pattern is to blame for Venezuela's water and power problems. But critics insist the state is also responsible for inadequate preparation, investment and diversification of electricity sources.

Maduro also said that from May 1, he planned to change Venezuela's time scheme as another way to save electricity.

"I'll explain that in the next few days," said Maduro, whose predecessor Hugo Chavez famously put Venezuela's clocks back half an hour in 2007 to allow children to wake up in daylight.

In a further bid to save energy, Maduro also decreed Monday a holiday, on top of a Tuesday national anniversary.

The president had already given public workers Fridays off, and raised eyebrows by urging women to cut usage of hair dryers.

The power problems have added to suffering from economic contraction, the world's highest inflation, shortages of basic goods, and lengthy lines at shops around the nation.

The opposition coalition is trying to oust Maduro via street protests or a referendum to end his six-year term.

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One opposition leader, Henrique Capriles, said the president was giving holidays not because of the power situation but to delay the formal steps needed to trigger a referendum.

"He will end in the rubbish-bin of political history," Capriles scoffed on Twitter. "As he has never liked working, he wants the whole country to be like that."

(Reporting by Andrew Cawthorne; editing by Alan Crosby and Andrew Hay)