It sounded like a deadline that a sheriff in a bad Western would issue.

On Thursday, state air quality officials gave Harvard representatives until noon Monday to present an argument for why the state should not disapprove the plans for Harvard's Medical Area Total Energy Plant project.

The stakes are high. Evidently expecting to receive the go-ahead, Harvard has already directed the engineering firm handling the $109 million project to dig up a city block and pour the foundation. The site has been swarming with workers in the past months.

On the other side, resident groups from neighborhoods near the power plant have been lobbying for the State Department of Environmental Quality Engineering to block the project.

Although the partially-constructed plant has been the focus of a prolonged controversy involving angry residents, critical public health researchers and the giant utility company Boston Edison, the idea behind the total energy plant is appealing in its simple rationality.

By combining in one facility the production of steam, chilled water and electricity, project planners expect to produce usable energy very efficiently, and to pass the savings along to the Medical School and affiliated hospitals.

Project planners hope the project will enable affiliated hospitals to reduce bed costs by two to three dollars a day.

But the diesel engines needed to produce electricity will also be sources of nitrogen dioxide, and unless Harvard representatives can show that the plant will not add excessively to the atmospheric level of the gas in the area, the environmental quality department will probably require elimination of the diesel generators from the project, entailing a major redesign.

One overhaul of the plant's design, before the foundation was laid, has already resulted in a one-to-two year delay in construction, and attendant costs.

But Dr. Anthony Cortese, director of the state division of air and hazardous materials, said yesterday the state had allowed Harvard to start work on the foundation with the understanding that it could not later plead financial hardship in seeking final approval.

Cortese said, "The plant will not be built if we believe it will have an impact on public health."