By Ahmed Elumami

TRIPOLI (Reuters) - Libya's U.N.-backed government is moving to tackle chronic power outages in a key test of the Tripoli-based administration's ability to take executive control and win support by improving living conditions.

Persistent power cuts lengthened during the Muslim fasting month of Ramadan that ended in early July, making life even more difficult for residents facing searing summer heat, cash shortages that delay salaries and continued lawlessness.

Tripoli residents express frustration that the Government of National Accord (GNA) has not acted more swiftly since arriving in the seaside capital at the end of March.

The result of a U.N.-mediated deal signed in December, the GNA was meant to replace two competing administrations set up in Tripoli and eastern Libya in 2014 and to end conflicts between the loose alliances of armed groups that supported them.

But it has failed to win formal backing from the east and has worked cautiously in Tripoli, moving gradually from a secured naval base into ministry buildings in town and only taking full possession of the prime minister's office last week.

Along with cash crisis and a spate of kidnappings, the power cuts have become a symbol of the limits of the GNA's authority in a city where real power lies largely with armed groups formed during the 2011 uprising against Muammar Gaddafi and its aftermath.

"The situation in Tripoli is getting worse day by day," said Khaled Delawi, a passport office employee shopping in the capital. "There is no power for long stretches, no money in the banks and no security. We hear every day of clashes and crimes but there's no response from the new government."

OUTAGES OUT OF CONTROL

Libya's national electricity company GECOL said last week the outages were "outside our control" because armed groups were diverting power supplies to their own neighborhoods – a problem acknowledged by GNA leader Fayez Seraj last month.

"There is also an absence of maintenance and security, and clashes in some areas badly affect the work of the company," GECOL said in a statement.

But after demonstrations escalated in central Tripoli, with protesters burning tyres in the street and building sand barriers to shut down a stretch of the coastal road, Seraj on Sunday sacked GECOL's entire board, replacing it with a caretaker team.

The interior ministry is also moving to secure power distribution control centers, said Mohamed Ammari, a member of the GNA's Presidential Council, to prevent distortions of the power supply by local factions or armed groups.

"We're dealing with it," he said.

He added that things had improved in recent days because a fall in temperatures had allowed more efficient power generation and GNA-aligned forces had partly retaken and restarted a power station in the coastal city of Sirte that had been seized by Islamic State militants last year.

Still, the situation remains precarious, with an average shortfall in national power supply that Ammari said stood at about 1,400 MW. Temperatures are likely to rise again in August, increasing demand for air conditioning.

And the recent cuts lasting 15 hours or more have stretched patience to breaking point, rotting food in disconnected fridges, forcing some shops to close down, and making the rumbling of generators familiar background noise across Tripoli.

"We have three governments but no services at all," said Tripoli shopkeeper Mohamed Ibrahim.

"The authorities, especially Seraj and his Council, must make big and urgent decisions to find solutions to all these problems. It's more than we can take."

(Additional reporting and writing by Aidan Lewis; Editing by Tom Heneghan)