"The area surrounding the proposed facility at Lamb's Knoll has significant scenic, cultural and natural resources. It is our duty to protect and restore the scenic beauty of this historic landscape," he wrote.
Rosa said he believes a compromise can be found.
Glendening's letter went to the Maryland Department of Budget and Management, which was going to build the tower, and the Maryland Department of Natural Resources, which owns the mountaintop land.
Thomas H. Miller, director of communications for the Maryland Institute for Emergency Medical Services, has argued that a tower of that size is needed to improve public safety communications.
He could not be reached Friday to comment on Glendening's letter.
In addition to the institute, the tower would serve the National Park Service and 911 communications for Washington and Frederick counties.
On July 16, the Harpers Ferry Conservancy asked the Federal Communications Commission to conduct an environmental assessment of the proposed tower.
On July 22, the FCC told state officials to delay the project until the agency could be satisfied the tower complies with environmental standards.
Preservationists say they had little notice the tower was going to be built.
"Somebody in Annapolis just didn't think. I'm glad the governor is forcing them to discover their brain," said Dennis Frye, a Civil War historian who said such a tall tower would intrude on the Antietam Battlefield's landscape.
Lamb's Knoll is the site of three other towers, all less than 100 feet tall. Rosa said he hopes to persuade the towers' owners to make them less obtrusive.
A 90-foot fire tower built in 1934 is no longer in working condition and could be removed, he said.
AT&T owns a microwave tower that dates from the 1950s. Rosa maintains it could be replaced by newer technology.
The third tower, owned by the federal government, is encased in a concrete bunker because it was built in the 1950s to withstand nuclear attack, he said. Rosa believes the Federal Aviation Administration is using it for backup communications.