VEHICLES registered in Hong Kong after April next year will have to comply with more stringent pollution standards under a proposed amendment. The standard would be in line with those adopted in the United States, Britain and Japan, said the Secretary for Planning, Environment and Lands, Tony Eason. Subject to consultation, the amendment regulation should be enacted by the third quarter of this year. He was confident vehicles capable of meeting these standards would be available in the territory. Mr Eason said air pollution in the main urban areas was mainly caused by ''light duty'' vehicles such as taxis and public light buses. He said pollution laws were being amended to require vehicles to use better quality fuel. The bill, which would enable this to be done, was introduced into the council for first reading in December and is due for a second reading on March 30. The administration was also considering introducing unleaded petrol with the aid of catalytic converters for light diesel vehicles. Early introduction of unleaded petrol was found to be impractical because the oil companies would be forced to buy petrol from the spot market instead of the traditional suppliers and hence the price would be much higher and the supply might be unstable,Mr Eason said. More vehicles would be examined for possible breaches of pollution laws and the Government would consider what might be done to halt the problem of pollution caused by the illegal use of sub-standard diesel by container lorries. The Government's targeting of light-duty vehicles came despite a study by Hong Kong University which found the biggest polluters on the road were trucks. According to the study, trucks, largely carrying goods to and from China, accounted for 48 per cent of nitrogen oxides and 39 per cent of particulates in 1992, and the figures were rising. The study suggested the Government was targeting the wrong group and it would have a bigger impact on air pollution if more effort was put into controlling trucks' emissions. Taxis, large buses, public light buses, light goods vehicles and cars accounted for the rest of the pollution. In reply to the study, the Environmental Protection Department said it was tackling pollution caused by large vehicles by adopting the most stringent emissions standards progressively introduced in Europe. It was also bringing into Hong Kong cleaner fuels, said Raymond Leung, the department's Assistant Director (Air and Noise).