* Authorities say youths threw stones at cars
* Protests rumble ahead of parliament election
* Vote seen as test of president's democratic mettle
By Saliou Samb
CONAKRY, Feb 19 (Reuters) - Security forces clashed with youths throwing stones in Guinea's capital on Tuesday as opponents of President Alpha Conde began a nationwide strike to demand a corruption-free election.
The strike began a day after street protests by opposition groups who say preparations have been flawed for the May 12 parliamentary vote, the first in a decade and a test of Conde's democratic credentials after the West African state emerged from two years of violent military rule.
The election will also be watched by major donors such as the European Union, which warned in November that it needed a credible and detailed timeline for the vote to unblock about 174 million euros ($232 million) for the impoverished country.
Much of the capital Conakry appeared unaffected by the strike on Tuesday, but in neighbourhoods seen as be opposition strongholds, shops closed and there was little road traffic.
Conakry residents said the clashes took place in three of those opposition neighbourhoods - Koloma, Bambeto and Bomboli.
"We've received several calls about a number of arrests," said Thierno Maadjou Sow, president of the Guinean Organisation of Human Rights. "We learned that one entire household was arrested following skirmishes between the youths and the security forces."
Koloma resident Abdoulaye Diallo said police beat a group of youths at the market in Koloma, arrested some and used tear gas to disperse the rest.
A spokesman for the security forces said they had acted after the youths began throwing stones at moving vehicles to punish their drivers for ignoring the strike call.
"That has nothing to do with a stay-at-home strike. These are delinquents who were arrested, not protesters," Commander Mamadou Alpha Barry said. "We are carrying out arrests to prevent these people from doing harm, but they will be freed once calm returns."
It was unclear how many arrests were made and no injuries were reported as a result of the clashes.
Conde was elected in 2010 in Guinea's first free poll since independence from France in 1958, ending the rule of a military junta that had seized power after the death of long-time leader Lansana Conte in 2008.
Conde has promised prosperity for Guinea's 10 million people, whose economy produces only about $1.50 per person per day despite a wealth of natural resources, including the world's largest untapped iron ore deposit.
Delays in holding the legislative vote, the last step in the transition from military rule, have deepened political deadlock and sparked intermittent violence, unnerving investors seeking to tap Guinea's abundant iron, bauxite and gold reserves.
The opposition accuses the president's allies on the elections commission of acting unilaterally in fixing the date of the polls and say two companies contracted to update voter rolls have skewed the lists in favour of Conde's allies. ($1 = 0.7487 euros) (Writing by Joe Bavier; Editing by Tom Pfeiffer)