Pro-democracy activists accused the ruling party Tuesday of harassment after police refused to give them permission to hold a mass rally this weekend. Vernon Mwaanga, a spokesman for pro-democracy campaigners, charged that ruling party officials have intimidated opposition supporters. He said ``thugs and hooligans'' tore down posters announcing upcoming rallies. Mwaanga described the postponement of Saturday's rally as an attempt to frustrate the opposition campaign for a multiparty democracy in this one-party state. The rally was rescheduled Sept. 8. Mwaanga said heads of the Frontline African states bordering South Africa are to meet in Lusaka on Saturday and police said they did not have the manpower to supervise both events simultaneously. ``It has been a consistent feature of our campaign that the authorities have frustrated our efforts to hold meetings,'' Mwaanga said. In a separate press statement Tuesday, Arthur Wina, chairman of the National Interim Committee for Multiparty Democracy, said he was disappointed that the government ``continued to operate on the basis of giving priority to foreign and international images rather than domestic affairs and national welfare.'' Earlier Tuesday, a longtime political associate of President Kenneth Kaunda said he would aggressively campaign to end one-party rule. Legislator Humphrey Mulemba, a former ruling party secretary-general, told reporters in Lusaka the scrapping of the one-party system was vital for the future well-being of Zambia, one of Africa's poorest nations. ``It is time we had political structural changes by removing one-party and introduce multiparty politics in Zambia,'' he said. As secretary-general of the ruling party for four years, Mulemba was No. 2 in the party hierarchy after Kaunda. He is the second ruling party legislator to openly attack one-party rule. ``With immediate effect I am going public and I am appealing to all Zambians for support,'' he said. Kaunda imposed a one-party system in 1973, when his ruling United National Independence Party became the only legal political organization in Zambia. Mulemba blamed one-party rule for ``inertia, corruption and lack of competition.'' On Monday, Frederick Chiluba, head of the powerful Zambia Congress of Trade Unions made his strongest attack yet against the ruling party. Addressing pro-democracy supporters, Chiluba accused Kaunda of being a dictator and criticized the ruling party for being out of touch with the people. A referendum on the political future of Zambia is scheduled Aug. 13, 1991.