ABOUT 100 people joined a petition organised by the United Democrats of Hong Kong (UDHK) yesterday to urge Governor Chris Patten to stand by his political reform package. Participants gathered at Chater Garden and marched to Government House to present their petition letter. Party vice-chairman Yeung Sum said Mr Patten's package was the least they would accept. He said the party was disappointed an agreement had not been reached between China and Britain on Hong Kong's political development despite 12 rounds of talks. Mr Yeung said a referendum should be held on any agreement reached between the two countries on the electoral arrangements. ''We cannot eliminate the possibility that Britain wants to reach an agreement in order to maintain a good relationship with China,'' he said. ''Even if there is an agreement, I think it should be voted on by the public to see if it is acceptable or not. ''Only then can we guarantee that the public will not be betrayed,'' he said. Another United Democrat legislator, James To Kun-sun, said Mr Patten would have to set a timetable on how to conduct the 1994/95 elections in his upcoming policy speech. ''By the time the Governor delivers his third policy speech in October 1994, we will have already finished the district board elections. How can a government be a responsible one if it does not have a substantial plan for the elections in this year's policy speech?'' he said. Mr To said the Government should make sure there would be enough time for potential candidates and voters to prepare for the elections. ''If we don't have the technical arrangements in place to go with the progress of the Boundary and Election Commission, that will be detrimental to the participation of local people in the elections, and that will indirectly affect the stability and prosperity of Hong Kong,'' he said.