Ho Chi Minh City in Vietnam, plagued by pollution but determined not to be consumed by it like Bangkok, is about to approve a five-year cleanup plan. Some 1,500 large industrial firms and more than 32,000 small industries are based in this city of 7 million, and they don’t filter their emissions. The new plan will let them gradually adapt to new rules, and a $1 million annual fund established last month will help educate companies about new pollution-control technologies. About 100 large state companies have signed a deal with the city to cut their pollution by 50 percent by the end of 2000. The Asian Development Bank plans to lend the city $70 million by 2003 to treat household sewage and set up an air-quality monitoring system.