WORK ON GREEK ALUMINA PLANT TO START END MAY Preparatory work for construction of a 450 mln dlr alumina plant near the village of Aghia Efthymia in the Greek province of Fokida will begin at the end of next month and the plant will be operational by 1992, Industry Undersecretary George Petsos said. Greece yesterday signed contracts with the Soviet Union for the joint venture project, the biggest investment in the country for 20 years. Petsos said the Soviet Union, which had initially agreed to buy 380,000 tonnes, would now purchase the plant's entire output of 600,000 tonnes a year.