* Thousands flee Greek fires fanned by strong winds
* Fires a test for conservative government
* Foreign help arrives but flights suspended
(Updates with fire receding, fire-fighting planes suspended)
By Renee Maltezou and Dina Kyriakidou
ATHENS, Aug 23 (Reuters) - A huge wildfire fanned by strong winds cut a swathe of destruction near Athens on Sunday, burning houses, razing large patches of forest and sending thousands fleeing their homes, authorities said.
Efforts to fight the blaze from the air were suspended as night fell and the fire raged unchecked for a third day, testing state resources and the conservative government, which is facing the threat of an early election by March.
"The constant shift in the wind's direction is rekindling the flames," said fire brigade spokesman Giannis Kapakis. "We must all remain calm through this night."
Authorities said the fire had retreated from Athens suburbs and was burning mainly forest land, but winds remained strong and the danger for a flare-up was constant.
"It will be a difficult night because everyone is exhausted," said Leonidas Kouris, governor of the eastern Attica region where a state of emergency was declared on Saturday. "We will keep fighting for another day," he told Greek TV.
Earlier on Sunday, local authorities used loudspeakers to urge the 20,000 residents of affluent Athens suburb Aghios Stefanos to leave as the flames approached.
Many people abandoned communities around Athens overnight and some frantically tried to stop the flames reaching houses with garden hoses and tree branches.
"We are facing a great ordeal," said Prime Minister Costas Karamanlis, who took a helicopter tour of the afflicted area. "The fire department is making a superhuman effort."
The handling of the fire, the biggest since Greece's worst wildfires in living memory killed 65 people over 10 days in 2007, will be crucial for his political fate.
His government is clinging to a one-seat majority and the socialist opposition, ahead in opinion polls, has made clear it will use a March parliamentary vote, when a new president will be chosen, to force a snap election.
"Nobody has learned anything from the big fires of 2007," far-right LAOS party leader George Karatzaferis told reporters. "It is a huge disaster and coordination was not the best."
STATE OF EMERGENCY
In eastern Attica the flames seared about 30,000 acres (12,140 hectares) of forest, farm fields and olive groves.
"A significant part of forest has been lost," WWF Greece conservation director Constantinos Liarikos told Reuters. "This fire will surely affect the Athens region's microclimate."
Help from Greece's European Union allies has started to arrive. Two Italian aircraft joined fire fighting efforts and more were expected from France and Cyprus.
The Greek weather service warned that winds hindering fire fighting efforts were not expected to abate before Monday night. Police and witnesses said scores of homes were heavily damaged.
The fire broke out late on Friday in the village of Grammatiko about 40 km (25 miles) northeast of the Greek capital and quickly spread to neighbouring villages. A children's hospital and a home for the elderly were evacuated.
Twelve aircraft, eight helicopters, 136 fire engines and about 644 fire fighters battled the blaze, fire officials said. Some 500 soldiers were also dispatched to the fires.
Summer fires are frequent in Greece, often caused by high temperatures and winds, drought or arson. In the last three days, more than 200 fires have broken out, some on the islands of Zakynthos, Evia and Skyros, and in the central Viotia area.
Hundreds of fires across southern Europe in July destroyed thousands of hectares of forest and gutted dozens of homes.