- Toll rises from persistent heat wave
* Putin orders arms sites, vital facilities protected
* Moscow gasping for air in smog
By Gleb Bryanski
MOSCOW, Aug 2 (Reuters) - Russia's leaders declared a state of emergency on Monday in seven provinces and ordered authorities to guard weapons storage facilities from wildfires that have killed at least 40 people.
Thousands more have lost their homes to blazes stoked by Russia's worst heatwave since the tsarist era. The heat has parched crops in one of the world's largest grain exporting nations, helping drive global grain prices to 22-month highs.
"Many families have nothing left -- the flames destroyed everything," President Dmitry Medvedev said in a sober announcement on state television. "It is a huge tragedy."
With little relief expected this week, he urged Russians to take care in tinder-dry forests and fields, warning that "every match tossed away could lead to irreparable disaster". Medvedev's emergency decree covered European Russian regions from Voronezh in the south to several Volga River areas and the densely populated province ringing Moscow.
A blanket of acrid smog covered the sweltering capital itself, worsening the woes of Muscovites gasping in Russia's hottest weather since record-keeping began around 1880. Some wore facemasks to filter the air they breathed.
Prime Minister Vladimir Putin ordered authorities to protect weapons sites, power plants and other vital facilities.
"The last thing we need is for arms stores to fall into this zone (affected by fires)," Putin said at a meeting with emergency officials and governors of affected regions.
Authorities said they had increased the number of firefighters near an iconic nuclear research centre by tenfold, but a spokesman for Russia's state nuclear corporation Rosatom, Sergei Novikov, said the centre was not currently in danger.
The facility at Sarov in the Nizhny Novgorod province around 350 kilometres (220 miles) east of Moscow was a top-secret location in Soviet times codenamed Arzamas-16, where the first Soviet atom and hydrogen bombs were designed.
"At the present time, all the fires around (the centre) have been put out so there is no threat to the nuclear centre," Novikov said. "There may be a threat of further fires from the south but special groups are prepared for that contingency."
RECONSTRUCTION
Putin warned that small blazes in areas where fires have been extinguished could be whipped up by winds and spread again. "Everything must be put out," Putin said.
Putin is still widely seen as Russia's top leader after steering Medvedev into the presidency in 2008 and is eager to retain his popularity ahead of elections in the next two years. He chided regional officials and demanded detailed accounts of plans to fight the fires and compensate the victims.
"You know what citizens are saying: 'Yes, we call (the authorities), but they hang up on us -- nobody wants to talk," Putin said at the meeting, shown in part on state television.
He ordered governors to report to him with timelines for the construction of housing, demanding information about "every region, every town, every home."
Medvedev said all those who have lost their homes must have roofs over their heads before winter.
Putin said compensation and reconstruction was expected to cost 5 billion roubles ($165 million). It will all come from the state budget because very few Russian households have insurance.
He also called for plans to prevent such losses from wildfires in the future. More people die per capita in household fires in Russia than in most Western nations because of poor infrastructure, flouting of safety rules and negligence.
Nearly 700 wildfires were burning on Monday over 1,210 square kilometres (750 square miles) of land, a spokeswoman for the Emergency Situations Ministry told Reuters.
The death toll rose from 28 people on Sunday to 40 on Monday, the Health Ministry said in a statement. (Additional reporting by Ludmila Danilova and Guy Faulconbridge and Sergei Karpukhin; writing by Alexei Anishchuk, Steve Gutterman; Editing by Jon Hemming)