PORTSMOUTH, N.H. – The federal government has committed $20 million needed to proceed with the replacement of the 88-year-old Memorial Bridge between Portsmouth and Kittery, Maine, officials said Wednesday.

Maine and New Hampshire will contribute $38.5 million apiece to replace the bridge, which carries U.S. 1 traffic over the Piscataqua River. Estimated total cost is $90 million.

U.S. senators from both states on Wednesday announced that the Department of Transportation had dedicated the $20 million, which was announced last fall by U.S. Transportation Secretary Ray Lahood before federal budget problems jeopardized the bridge funding.

Maine and New Hampshire officials agreed last year to replace the Memorial Bridge. Construction, which begins in mid-2012, is expected to take 18 months.

Replacing the bridge “is crucial to the flow of goods, services and people between Maine and New Hampshire, and for keeping and attracting new jobs to this region,” said Sen. Susan Collins, R-Maine, who sits on the transportation appropriations subcommittee.

In addition to replacing Memorial Bridge, Maine and New Hampshire must rehabilitate Sara Mildred Long Bridge and do maintenance on the I-95 bridge. The cost of all three projects over the next 30 years will be about $500 million, officials have said.

Memorial Bridge, which was closed to traffic for more than a week in December because of structural concerns, is the most immediate problem. The bridge’s weight limit was reduced in 2009, and last summer a tug operator said a giant chunk of steel fell from the bridge.