MONTPELIER, Vt. — Vermont’s largest hospital is working with a New Hampshire hospital that runs a helicopter ambulance service to expand it to help move critically ill or injured patients between hospitals in Vermont and upstate New York.

The plan by the University of Vermont Medical Center in Burlington and Dartmouth-Hitchcock Medical Center in New Hampshire is part of a broader effort to improve the transportation system for the hospitals UVM serves.

“This has long been a dream of many, many previous leaders here in the organization,” said University of Vermont Medical Center President Eileen Whalen.

Some patients already are moved by helicopter between the hospitals in the University of Vermont network or to other facilities, but they are not consistent.

UVM’s 40,000-square-mile service area reaches from the New York communities of Massena and Canton to the west or Newport in northeastern Vermont.

But for many medical emergencies, such as strokes and heart attacks, time can make all the difference in outcome, Whalen said.

A helicopter can reduce travel time between the hospitals from hours to less than an hour.

The UVM Medical Center is working with Dartmouth-Hitchcock to expand the air ambulance service known as the Dartmouth-Hitchcock Advanced Response Team.

“The collaboration is anticipated to build on the DHART program and also to utilize specialized UVM Medical Center clinical staff,” said Dartmouth-Hitchcock spokesman Michael Barwell.

UVM and Dartmouth-Hitchcock are continuing to negotiate. Whalen said she expects a finalized deal before the end of the month. Current plans call for beginning the expanded air ambulance service sometime next year, she said.

The Lebanon, New Hampshire-based Dartmouth-Hitchcock currently bases helicopter ambulances in the New Hampshire communities of Lebanon and Manchester.

The helicopters regularly carry patients between Vermont hospitals and other regional facilities as warranted.

UVM officials said it’s too early to know how much the added service would cost.