* Politician denies hitting '120 to 130 kg' policeman
* Ruling coalition depends on support from nationalist party
By Angel Krasimirov
SOFIA, March 12 (Reuters) - Bulgarian nationalist party leader Volen Siderov was charged with hooliganism on Wednesday over his alleged involvement in an airport scuffle in January, in a politically sensitive case for the country's fragile coalition government.
Siderov, 57, denies injuring a male passenger and a policeman in an incident on a runway bus at the airport in the Black Sea city of Varna. If convicted, he could face up to five years in prison.
The coalition of the Socialists and the smaller ethnic Turkish MRF party is two seats short of a majority in the 240-member parliament and has to rely on the unofficial support of Siderov's Attack party, which has 23 deputies.
The white-haired Siderov described the pre-trial proceedings as "strange" and said he would testify after four Attack deputies, who witnessed the alleged fracas, are questioned on Friday.
"I insist that a trial begins as soon as possible so that things become clear," he told reporters outside the Sofia Investigative Service.
Former journalist Siderov denied hitting the policeman.
"The officer weighs some 120 kg to 130 kg (265 to 285 lb) and did martial arts, while I weigh some 70 kg with clothes on," he said.
Earlier on the day of the alleged incident, Siderov had got into a row on a plane with the female cultural attache at the French Embassy in Sofia, prompting the embassy to condemn what it called his aggressive behaviour.
Two weeks later, he waived his immunity to show he was ready to defend himself against prosecution, and Attack's 22 other deputies also gave up theirs in solidarity.
Siderov has gained popularity in recent years with populist pledges to improve the lives of poor Bulgarians. Attack wants to nationalise energy distributors, raise taxes on the rich and revoke concessions for gold and water granted to foreign companies. It blames the "colonial" West for low wages and high prices in the European Union's poorest member state.
Bulgaria has been criticised by the EU for failing to show tangible results in imposing the strict rule of law and fighting organised crime and corruption. (Reporting by Angel Krasimirov; Editing by Mark Trevelyan)