PRESSURE is mounting on China to stipulate a set of clear guidelines for legislators to ride the through train to the 1997 legislature. The call came from legislators who want China to set out its requirements for boarding the through train when the issue is raised between Beijing and London at Sino-British talks on Thursday. A majority of members, representing the major political factions in the Legislative Council, told the South China Morning Post that they would like the guidelines to be clear and simple. China should not settle old political scores in deciding who keep their seats in the post-1997 legislature, they said. The legislators joined earlier calls by British officials including the Governor, Mr Chris Patten, for Beijing to disclose at the talks its criteria, if any, for screening candidates. The pro-Beijing Democratic Alliance for the Betterment of Hongkong is to call on China to draw up ''clear and predictable'' criteria and the alliance will set out its own guidelines today. Although most legislators acknowledge the legitimacy of the future Special Administrative Region (SAR) Preparatory Committee in confirming legislators' rights to a seat, they stressed that it must not be used as a means to oust ''unwelcome'' politicians. Under the Basic Law, members elected to Legco in 1995 who uphold the mini-constitution and pledge allegiance to the SAR government may, ''upon confirmation by the Preparatory Committee'', become members of the first post-1997 legislature. United Democrats' chairman Mr Martin Lee Chu-ming said it was necessary for the two governments to clarify the provisions in the Basic Law during Thursday's talks. ''I think it will be best for the two sides to agree that anyone who is elected in 1995 can stay in the first SAR's legislature,'' he said. ''What is meant by upholding the Basic Law? What is meant by pledging allegiance to the Basic Law? I think the two governments should clarify this.'' Fear of being ejected from the SAR legislature by arbitrary mainland conditions could make some members impotent, he said. But the criteria must not exceed provisions in the Basic Law or Beijing ran the risk of usurping the power of the future SAR. Meeting Point's Mr Fred Li Wah-ming said the criteria should be kept to a minimum and only cover objective requirements such as the age and criminal records. ''They should not include too much of a political element which is often subject to individual interpretations,'' he said. It was a view shared by the chairman of the Association for Democracy and People's Livelihood, Mr Frederick Fung Kin-kee. He suggested conditions for qualification be put into law to be enacted in 1997. Pro-China legislator Mr Tam Yiu-chung insisted that it should be left for the two governments to discuss the details and that no one should be rejected before 1997. ''No one is in the position to make the judgement as to who should be allowed to board the train before the Basic Law comes [in] in 1997,'' he said.