* Soldiers try to protect Serbian power plant
* River Sava expected to keep rising
* Russia sends food, rescue boats (Updates toll, adds details; changes dateline, pvs BELGRADE)
By Fedja Grulovic and Zeljko Debelnogic
OBRENOVAC, Serbia/DOBOJ, Bosnia, May 18 (Reuters) - Russian cargo planes and rescue teams from around Europe on Sunday joined huge volunteer aid efforts in swathes of Serbia and Bosnia where at least 24 people have died in the worst floods in over a century.
Rains eased and waters receded in the worst-hit areas of central and western Serbia and northeastern Bosnia, but the River Sava was forecast to continue rising in the Serbian capital, Belgrade.
The Sava burst its banks after days of torrential flooding in the ex-Yugoslav republics, flooding towns and cutting power to tens of thousands of homes.
Thousands of soldiers and volunteers worked through the night to build a sandbag barrier five kilometres (3 miles) long to protect Serbia's Kostolac coal-fired power plant, which currently covers 20 percent of Serbia's electricity needs.
But waters from the River Mlava broke through early on Sunday, threatening the Drmno coal mine deposits near the Kostolac plant.
"The army, police, volunteers and Kostolac employees are using all mechanisation and are piling up sandbags to slow the river flow and prevent it from entering the power generation system," Alma Muslibegovic, a spokeswoman for Serbia's EPS power distributor, told Reuters.
Flooding had already cut Serbian power generation by 40 percent, forcing the cash-strapped Balkan country to boost imports.
Prime Minister Aleksandar Vucic said a fire and flooding of surface mines at the 1,300 megawatt (MW) Kolubara coal-fired power plant southwest of Belgrade had caused damage of "at least 100 million euros ($137 million)".
Authorities say the economic impact of the floods will be huge, devastating the agricultural sector vital to both the Serbian and Bosnian economies.
"The danger today is less than it was yesterday, but we have to control the Sava as much as we can," Vucic told a televised cabinet session. "These are the kind of waters not seen in 1,000 years, let alone 100."
Vucic said two bodies had been recovered from the worst-hit Serbian town of Obrenovac, some 30 km southwest of Belgrade, the Tanjug news agency reported.
Predrag Maric, the Interior Ministry's head of emergency situations, said the death toll in Serbia so far was five, with one person missing. The toll was expected to rise.
In Obrenovac, members of a rafting club from the southern Serbian town of Raska joined rescue efforts, evacuating elderly men and women on their backs after days spent without electricity in flooded homes.
In Bosnia, 19 people were confirmed dead by Saturday, with nine bodies recovered from the northeastern town of Doboj after what the regional police chief described as a "tsunami" of water 3-4 metres (10-13 feet) high.
A Reuters cameraman at the scene said half the town was still submerged. Bosnian soldiers distributed food and medical supplies by truck, boat and bulldozer. Cranes lifted medical workers into the top floors of some homes and removed stranded residents from others.
On Sunday, two Russian Ilyushin-26 cargo planes landed in Serbia carrying food, generators and rescue boats.
Rescue teams, humanitarian aid, water pumps and generators have arrived from Russia and several European Union member states, including Britain, Germany and Austria. Support has also come from Serbia and Bosnia's fellow ex-Yugoslav republics.
Some 20,000 people have been evacuated in Serbia and at least 13,000 more in Bosnia. Donations of clothes and food poured into collection centres in Belgrade.
"I carried my kids out on my back, then waited 12 hours to be rescued myself," said 40-year-old Obrenovac resident Dragan Todorovic, who spent the night in a Belgrade sports hall with dozens of other families. "The house was new, built two years ago for 100,000 euros. What now?"
($1 = 0.7297 Euros) (Additional reporting by Daria Sito-Sucic and Maja Zuvela in Sarajevo, Matt Robinson in Belgrade; Writing by Matt Robinson; Editing by Sophie Hares)