* Traffic slowly resumes on Athens subway lines
* Subway workers' strike went into ninth day
* Police break up occupation of subway train depot (Recasts with end of strike, minister, union comments)
By Karolina Tagaris
ATHENS, Jan 25 (Reuters) - Striking Greek subway workers trickled back to work on Friday after the government threatened them with arrest, ending a nine-day walkout that paralysed public transport in Athens.
The showdown had turned into the latest test for Greece's fragile three-party ruling coalition as it faces down unions to try to implement austerity measures demanded by foreign lenders as the price for bailout funds.
Traffic slowly resumed on Athens' subway lines on Friday afternoon after workers protesting wage cuts were served orders to return to work or face jail, the first time the government has invoked such legislation since it took power in June.
"The workers who were handed the notice didn't have a choice. We are exploring legal options," said Manthos Tsakos, general secretary of the main subway workers' union.
Earlier on Friday, police forced their way through a metal gate at a train depot in Athens to break up an overnight sit-in by 90 transport workers against wage cuts. Scuffles broke out and at least three people were detained before being released.
The radical leftist opposition Syriza party, which is leading in some opinion polls, said the police intervention was a "barbaric" attack on workers' rights.
Eager to show lenders and Greeks that it is determined to implement promised reforms, Prime Minister Antonis Samaras has taken a hard line on the strikers despite facing criticism from one of his own coalition partners.
"Under no circumstances can the government allow the country to be derailed and to let the sacrifices of the Greek people go to waste," Development Minister Kostis Hatzidakis, who oversees transport issues, said in a televised statement.
Other transport unions held strikes in solidarity with subway workers on Friday, leaving Athens without bus, tram, trolleybus or rail services, and causing gridlock across the city.
Traffic ground to a halt in the capital, fuelling public anger against the strike which affected more than a million commuters in a city of 5 million people.
"HARD TO HAVE SYMPATHY"
"This week has been hell. How can they expect people to be on their side when they do this to us? We're all suffering (from austerity) but it's very difficult to have any sympathy for them," said 50-year-old Dionisis Kefalas.
Other commuters, worn down by years of frequent strikes and exasperated by the long wait for a taxi to work, agreed.
"Ordinary people are being inconvenienced - as if our problems weren't bad enough," said Daphne Kiritsi, 46, an office clerk, who said she had paid 200 euros out of her 800-euro monthly salary for taxis this week.
Subway employees oppose being included in a unified wage scheme for public sector workers drawn up under an austerity programme that would slash their salaries.
Under the emergency law invoked, which is meant to be used in times of war, natural disaster or risks to public health, workers can be arrested and jailed for up to five years.
Subway, shipyard and other public sector workers planned to march on Friday to parliament in Syntagma Square, the scene of often violent protests in recent years.
The most powerful unions threw their support behind the subway workers.
"The workers' struggle will continue until justice is had," said Nikos Kioutsoukis, general secretary of the GSEE private sector union, which has called a 24-hour strike against austerity measures next month. (Additional reporting by George Georgiopoulos; Editing by Deepa Babington and Myra MacDonald)