The Obama administration will make nearly half a billion dollars available to states to create thousands of construction jobs and fix the nation’s aging infrastructure.

Transportation Secretary Ray LaHood said at a news conference Friday that more than $470 million would be made available to repair crumbling roads and bridges. The District of Columbia and Puerto Rico are also eligible for the funds.

The money comes from Congressional earmarks from 2003 to 2006 that were provided in the Transportation Department’s budget. Earmarks are provisions in spending bills that direct taxpayer dollars to pet projects in lawmakers’ districts or states.

“These idle earmarks have sat on the shelf as our infrastructure continues to age and construction workers sit on the sidelines. That ends today,” Mr. LaHood said.

Mr. LaHood said the money was never spent because states completed the projects without the money or the projects were abandoned before any work began.

The American Society of Civil Engineers estimates that the nation faces a $2.2 trillion infrastructure backlog. One of every eight bridges is “structurally deficient,” and 85 percent of public transit systems are struggling to carry a growing number of riders, the group said.

Under the Transportation Department plan, Mr. LaHood said states must identify how the funds would be used by Oct. 1.

The transportation funding announcement is part of President Obama’s election-year effort to bypass a Congress that has failed to pass several crucial pieces of legislation, including a transportation spending bill. Last week the Obama administration announced plans to buy $170 million worth of meat to help farmers struck by drought. The move came after Congress failed to pass a farm bill or a separate disaster bill that would have helped farmers and states hard-hit by the worst drought in 56 years.

Mr. LaHood played down the political implications of releasing the funds in the middle of an election campaign.

“During the first two years in office, we were focused on getting the $48 billion in stimulus money for construction and transportation projects spent,” he said. “We have been trying to find other money when we discovered that there was a large amount of money that had been earmarked.”

Earmarks were banned by Congress in 2010 after Republicans captured the House. The Senate followed with its own ban on earmarks.

Mr. Obama has also opposed earmarks, saying he would veto any bill that includes Congressional spending requests.