* Main parties declined chance to form government
* Bulgaria to have interim government
* More protests over electricity prices planned
By Tsvetelia Tsolova
SOFIA, Feb 22 (Reuters) - Bulgaria's president will appoint a caretaker government ahead of a parliamentary election by mid-May after protests toppled austerity-minded Prime Minister Boiko Borisov, the president said on Friday.
Wednesday's resignation by Borisov's rightist government has failed to quell anger in the European Union's poorest country over high utility bills and protesters gathered on Friday evening in the capital Sofia and other cities.
President Rosen Plevneliev said major political parties - including Borisov's GERB and their rivals the Socialists - declined the chance to form a new government and polls will be brought forward from the previously planned date in July.
"We are heading towards an interim government. We have agreed that the possible timeline for next elections will be the end of April until the middle of May," Plevneliev told reporters after consultation with political parties.
Frustration at low living standards led to bloody protests this month. Many in the Black Sea state of 7.3 million are angry Borisov failed to honour 2009 election pledges to cut corruption and reform inefficient healthcare and education systems.
The prime minister, a former bodyguard of late Soviet-era dictator Todor Zhivkov, ceded to pressure and his administration became the latest to fall in Europe's four-year-old debt crisis.
The president said he will appoint a technocratic caretaker government to focus on financial stability and free elections.
The outgoing parliament should work to change the energy law to cut electricity prices and defuse public anger, he said.
"This is the only possible and reasonable move," said Kantcho Stoychev, from pollster Gallup International. "If the president appoints a politically-linked cabinet, the people's anger will fall on him and may endanger the civil peace."
GERB is running neck-and-neck with the Socialists in opinion polls. With both at around 22 to 23 percent support, neither is expected to win a majority in the upcoming vote.
A hung parliament could lead to the type of policy stalemate that has stalled reforms in neighbouring Romania and Greece.
Since a sharp contraction in 2009, Bulgaria has failed to resume the rapid growth needed to catch up with EU partners. Living standards are about 45 percent of the bloc average.
On Friday, dozens of people protested against Czech power distributor CEZ in the northeastern city of Vratsa. Borisov promised an 8 percent electricity bill cut from March and said the regulator would begin to revoke CEZ's licence.
The energy regulator said a price cut is possible from April at the earliest and indicated room for compromise with CEZ.