AFTER weeks of pressure from environmentalists and left-wing politicians, Edmondo Angele, Rome's chief traffic official, has proposed measures to reduce pollution and ease traffic congestion in the capital's historical center.Most of Rome's nine pollution monitoring stations have been reporting higher-than-acceptable levels of carbon monoxide emissions since Romans returned from vacation in early September. To combat the problem, Mr. Angele seeks: * A ban on private traffic from 6 a.m. to 7:30 p.m. in the center of Rome, to take effect this coming Monday. The area includes Via Veneto, the fashionable and heavily trafficked street on which the United States embassy is situated. In addition, the center would be off limits during the hours of 10 p.m. to 1 a.m. on Fridays and Saturdays year round and every evening from June 15 through Sept. 15. Buses, taxis, and emergency vehicles would continue to operate in the area. * Elimination by Jan. 1 of half the 16,000 passes that allow privileged professionals to use the few city center streets already closed to private traffic. * Deployment of 1,500 policemen to enforce the rules. Although a poll published last week by La Repubblica newspaper showed that more than 90 percent of Romans agreed with the statement, "The traffic situation has become unbearable," no action has been taken so far. The City Council met Tuesday to vote on Angels plans, but postponed action when the session erupted in controversy. The Greens and the communists said the plan did not go far enough, while the conservative opposition called for less drastic action. Franco Carraro, Rome's mayor, has pledged to impose the measures until Christmas, if the council does not vote on them when it convenes again today. Environmentalists, meanwhile, argue more needs to be done. Rome's ban is similar to actions already taken in Milan, which have not substantially changed the levels of pollution in that northern commercial city says Roberto Della Seta, a spokesman for the Environmental League. He cites favorably the central Italian city of Perugia. "It's a small city where they have practically expelled automobiles from the city center." In Rome, the environmental league would like to see all private traffic eliminated from the city center at all hours, stronger support for public transportation (including creating automobile parking lots on the outskirts of city near bus and subway connections) and more streets and paths set aside for bicycles and pedestrians. Mr. Della Seta says that Environmental League research shows that air pollution in Rome is "a constant" emergency, not a temporary one. Della Seta notes that the virtual absence of catalytic converters, which remove toxic substances from car exhausts, adds to the pollution problem. Only 2 percent of cars in Italy have them, he says, versus 50 to 60 percent in Germany and Scandinavia. Italian manufacturers will not be required to offer them until Jan. 1, 1993, when the country will have to conform to European Community standards.