THE criteria upon which the Special Administrative Region (SAR) Preparatory Committee will vet legislators in 1997 should be put into law in order to enhance legal protection against arbitrary political screening in 1997, according to legal experts in Hongkong. The legal experts urged the British and Chinese governments to reach an agreement on the controversial through train arrangements at the bilateral talks so that legislation based on the pact could be enacted before the 1995 polls. Human rights legal expert Mr Johannes Chan Man-mun, a senior law lecturer at Hongkong University, warned the Bill of Rights could not provide sufficient legal protection against arbitrary political screening of the legislators in 1997 because the Basic Law would be superior to the bill after the handover. ''The more feasible resolution to resolve the through train controversy is to legislate a law before the 1995 elections to clarify the criteria for the vetting arrangements in order to increase the role of the courts,'' he said. ''Such a constitutional problem can only be resolved by the political process.'' Executive Councillor Mr Denis Chang Khen-lee, QC, said the SAR Preparatory Committee should be based on the law, which should stipulate objective criteria for the through train arrangements, when it acknowledged the legislators in 1997. ''No country in the world can accept elected legislators being simply asked to leave the legislature without the basis of a clear law,'' Mr Chang said. However, Mr Benny Tai Yiu-ting, law lecturer at Hongkong University, doubted Hongkong courts' ability to hear such cases. ''According to the Basic Law, Hongkong courts have no jurisdiction to hear cases involving acts of state of the central Government,'' Mr Tai said.