PORTLAND – Rail officials are taking advantage of a shutdown in Amtrak’s Downeaster service prompted by security for the Democratic National Convention to make weeklong track improvements.

Workers will use the shutdown of passenger rail service between Portland and Boston to complete a $900,000 track overhaul in Kennebunk intended to speed up the trip.

Trains had been forced to slow to 25 mph on that stretch of track, due to a weak clay foundation, said Patricia Douglas of the Northern New England Passenger Rail Authority.

Scores of heavy trucks will be hauling away the clay and returning with sturdier fill, Douglas said.

When the Downeaster resumes service on Aug. 1, the train will shave 5 minutes off the leg between Portland and Old Orchard Beach because the train will be hitting a top speed of 79 mph for the first time, Douglas said. Another 5 minutes will be shaved off the round trip when additional schedule changes are adopted on Nov. 1, reflecting the Kennebunk improvements, she said.

By fall 2005, the Downeaster will travel at 79 mph along a total of 30 miles, reducing the travel time between Portland and Boston to 21/2 hours, officials said. The full route now takes 2 hours, 45 minutes.

“There’s a lot of work being done and there are a lot of things coming together. It’s just not as easy as it appears. It’s a complicated process. There are different railroads involved,” she said.