CRITICISM over the enforcement of residency requirements under the electoral laws increased yesterday as the nominations of three more candidates for district board polls were rejected. Senior government sources said more nominations were likely to be disqualified for similar reasons, but denied that application of the residency requirement had been made stricter. They also warned that any amendment to the definition of ''ordinarily resident'' would be dangerous and bring about drastic changes to immigration laws. Dissident Lau Shan-ching, who spent 10 years in a Chinese jail from 1981 for his pro-democracy activities, had his election application rejected on Thursday, as did Danny Chin Ching-man, who spent six years in the United States studying and working. The three candidates rejected yesterday were Yeung Man-wai of Wong Tai Sin, Chan Po-ming of Tsuen Wan, and Yen Ho-yin of Shamshuipo. They said the decision was unreasonable and vowed to take their cases to court. The controversy centres on a provision in the electoral laws that says candidates must ''ordinarily reside'' in Hong Kong for the 10 years before an election. Citing his own case as an example, United Democrats legislator Albert Chan Wai-yip said the enforcement of the residency rule had been unfairly tightened for the upcoming district board elections. Mr Chan said he had been allowed to stand for the district board election in 1985 despite being absent from Hong Kong between 1972 and 1982. He said he had been told by the electoral office that there would be no problem with his eligibility. ''I even wrote on my handbills to tell the voters that I had been studying overseas for 10 years,'' he recalled last night. The chairman of the Association for Democracy and People's Livelihood, Frederick Fung Kin-kee, said some legislative councillors had also been elected to office despite extended stays overseas. ''I myself had been studying in Britain between 1979 and 1982. On my return in 1983 no one has challenged my validity,'' he said. ''There were so many precedents to show that the provision had not been enacted, why are they suddenly becoming so serious about it?'' The sources said the declaration of candidates' residency details were different for the upcoming election because of the establishment of the independent Boundary and Election Committee. But they denied the rules were being made ''stricter''. One source said: ''Candidates did have to declare that they met the residency requirements in previous elections. There were also cases where the residency status of candidates were in doubt. They were not made public after their status was cleared.'' The source said returning officers would seek advice from the Legal Department if they were uncertain about the residency status of a candidate. ''There is an object criteria based on the body of law including precedent cases. There is no mechanical criteria. And you can't have a mechanical interpretation of the term of 'ordinarily resident'. That is a concept used in immigration law, but not for elections. ''It will be dangerous if we change the law just for the sake of elections. There will be wide implications. ''The present law has been used for years. We can't make a conclusion now [on whether the law should be amended] in view of a couple of cases. It depends on what the Legislative Council and the public think in the review at the end of the election,'' the source said. Mr Chan, one of the three rejected yesterday, was hoping to stand as a candidate for the United Front for the Service of People of Hong Kong, which is headed by Yeung Fok-kwong. Mr Chan left the territory in May 1989. He returned in April this year after completing a five-year contract to organise and operate a newspaper in Canada. He was accompanied by his wife and two children during his stay in Canada, while his parents stayed in Hong Kong. Mr Yeung described the rejection of Mr Chan's nomination as ''extremely unreasonable'' and he called for the amendment of the electoral law on candidates' eligibility which gave room for loose interpretations. He said the chairman of the Boundary and Election Commission, Mr Justice Woo Kwok-hing, should be held responsible for the confusion. ''He has been wrong to allow this provision to remain, he has ignored the previous practices,'' he said.