TORONTO - More than a century ago, Canada forced tens of thousands of Chinese who helped build the nation's railroad to pay a "head tax" if they wished to remain in the country. Yesterday, Canada apologized. Five frail survivors who paid the head tax - the oldest is 106 - were among those at the atonement ceremony in Ottawa. The government also announced that it would pay compensation. The head tax, which started in 1885 at $50 and grew to $500 by 1903 - then two years' wages for Chinese laborers - ended in 1923, when immigration from China was banned. Canada began admitting Chinese again only in 1947.