Mattapan Crossing and Canopy Walk: A section of the proposed Neponset Greenway is depicted in a plan prepared by the DCR.In a major disappointment to state officials and community activists, the US Department of Transportation has passed over a grant application from the state's Department of Conservation and Recreation (DCR) to fund the expansion of the Neponset Greenway. The decision could further delay the completion of key elements of the popular Greenway trail, including two bridges in Mattapan that are considered essential to safely navigate a missing link of the trail in that part of Boston. Another key missing link on the trail in Dorchester near the landmark rainbow gas tank was also included in the grant application.

The US Department of Transportation announced the winners of its national TIGER III grant awards on Thursday, months ahead of schedule. The DCR had submitted its application seeking $10 million for the Neponset Greenway project in October and the timeline from the federal agency called for a decision in April 2012.

In an announcement posted on its website yesterday, the US DOT acknowledged that the awards — totaling $511 million in grants to 46 projects around the country— came "months ahead of schedule" to and "allow communities to move forward with critical, job-creating infrastructure projects including road and bridge improvements; transit upgrades; freight, port and rail expansions; and new options for bicyclists and pedestrians."

The agency noted that they received 848 applications requesting $14.29 billion in funding. The Neponset Greenway project was one of many that didn't make the cut.

Only one Massachusetts project was funded: The MBTA won a $10 million grant to fund construction of three bridges over the Merrimack River in Haverhill. The awards were distributed to projects in 38 different states and Puerto Rico, according to the US DOT. Illinois, the home state of President Obama, received the most of any state, with $44.3 million going to fund three different projects, including $20 million for a mass transit and bike sharing project in Chicago.

A spokesperson for DCR, SJ Port, said in an e-mail that the state agency is "dedicated to this project and plan to keep pushing for other sources of funding."

Valerie Burns of the Boston Natural Areas Network, the leading advocacy group for the Greenway, said there was a mix of reactions to the news.

"The advocates turned to our elected officials to let them know how important this was, but we knew that the odds were stacked against us and that this grant would be incredibly competitive," Burns said. But there was almost universal agreement that the Boston project fit the criteria so well. The decision process is a mix of substance and politics."

Burns added that she still feels optimistic that the state is committed enough to the project to keep fighting for other funds.

"One of the things that came out of this is that there's such momentum behind it within the [Patrick] administration and our elected officials and the community about how right this project is for this point in time and for this part of the city and Greater Boston," Burns said. "I am encouraged that we're not going to lose the energy that's been directed towards this project."