Five weeks of state hearings on the environmental effects of Harvard's $130 million Medical Area power plant project officially ended yesterday.

The state is expected to announce its decision on whether the University can continue to build the plant as it is currently designed in late January.

Harvard began construction of the plant in the Mission Hill-Brookline area of Boston in November 1976. The University has already spent more than $50 million on the project, which it hopes will provide steam, electricity and chilled water to the Medical School and Harvard-affiliated hospitals at an annual savings of $2 million.

The project ran into trouble last January when a state environmental agency ruled that Harvard could not install diesel generators in the plant because they would allegedly produce dangerous levels of the pollutant nitrogen dioxide.

The University appealed the ruling and requested the current hearings to reconsider the diesel issue.

Michael Lambert, a Mission Hill resident who participated in the hearings as an opponent of the power plant, said yesterday, "The fight seems to have boiled down to what level of nitrogen dioxide will be harmful to public health."

Both local opponents of the plant and the Massachusetts Department of Environmental Quality Engineering introduced experts at the hearings who testified that levels above 200 micrograms per cubic meter of nitrogen dioxide in the atmosphere will aggravate lung ailments and reduce immunity to disease, particularly among children and the elderly.

Lawyers for the University, however, also introduced national experts in environmental medicine who argued that nitrogen dioxide does not become dangerous until it reaches a level of at least 400 micrograms per cubic meter.

L. Edward Lashman, director of external projects for the University, said yesterday the power plant can meet the 400 microgram limit, and would not adversely affect public health.

However, Lambert said yesterday, "The community surrounding the power plant has a very high proportion of especially susceptible children and elderly people. This is a serious danger."