SALEM — Northshore Ambulance, which serves both Salem and Marblehead, is under agreement to be sold, the company said yesterday.

Atlantic Ambulance Service, a division of Somerville-based Cataldo Ambulance Service, has agreed to purchase the company and is expected to take over operations and 911 services in both Salem and Marblehead, said Northshore President and CEO Bob Dionne.

The sale had been in the works for about a month and comes just three months after Northshore lost its contract with Peabody; the city went with Atlantic instead.

"The financial impact of losing a contract of that magnitude, it hit us pretty hard," Dionne said. "So it was a decision that we made here to sell to a company that has a good reputation and that will do good by our contracts."

Cataldo had tried to buy Salem-based Northshore three times in the last 15 years but was unsuccessful until now, said Dennis Cataldo, vice president of Cataldo Ambulance.

"The communities of Salem and Marblehead are very strategically placed municipalities in our business plan," he said.

The company already runs ambulances in Peabody, Lynn, Saugus, Revere, Boston and other communities.

"We're really excited about this," he said.

The transition is expected to take about two months, and the company has already received verbal agreements from Salem and Marblehead to continue their contracts in their entirety, Cataldo said.

"There will be no interruption of services whatsoever," he said.

The company is purchasing Northshore's assets, not the corporation, which means it won't inherit any debt or any pending or future lawsuits against the company.

Northshore employees will have to reapply to Atlantic for their jobs. Northshore employs about 70 workers, mainly ambulance and wheelchair van attendants.

Both companies declined to reveal the sale price.