BANGOR – One of the city’s most familiar structures is scheduled to undergo major surgery.

Most visitors to the Margaret Chase Smith Federal Building on Harlow Street, however, won’t notice the $17.8 million infrastructure upgrade slated to begin in about two years.

U.S. Sen. Susan Collins, whose Bangor office is on the second floor of the three-story building, last month called the upgrade “long overdue” in a press release announcing the project.

“The Margaret Chase Smith building not only houses Bangor’s federal employees, but also serves the community as a post office and courthouse,” Collins said in the release. “This funding would allow for long overdue upgrades to improve the safety and function of the building as well as ensure that it complies with accessibility standards.”

The building is named for the late U.S. senator from Skowhegan who served 33 years in Congress.

The $1.6 million design stage – the first step in the project – is scheduled to begin later this year.

The most visible phase will be the conversion of 21,500 square feet of the former postal sorting area into office space, according to Amy Swanstrom, spokeswoman for Collins. Most of that space, located on the first floor behind the post office counter and lobby, has been vacant since 1994 when the Eastern Maine Processing and Distribution Plant opened and the mail sorting operation was moved to the new facility in Hampden.

About 7,000 square feet of the former post office area in the building on Harlow Street was converted three years ago into offices for the U.S. attorney’s Bangor staff. The remaining space is not expected to be ready for occupancy until 2007 or 2008. The tenants have not been selected, although rumors about which agencies might occupy the first-floor offices already are circulating throughout the building.

The U.S. post office will not be moving.

During the renovation phase, other agencies may have to move temporarily to empty offices in the building, according to the General Services Administration, which is in charge of the facility.

The building, which has a total of 165,897 square feet, according to Collins’ office, was constructed at a cost of $4.5 million between 1966 and 1967 and opened in 1968. Currently, 15 federal agencies are housed in the building.

Major upgrades to the heating, air conditioning and electrical systems have not been made since then, according to the GSA. The infrastructure work will include upgrades of those systems as well as renovations to increase energy and water conservation.

Other work will improve the availability of water to firefighters during a potential blaze by making water pipes accessible in all the stairwells. Sections of the building that do not meet accessibility standards for the disabled also will be modified, according to the GSA.