Susannah Morgan, executive director of the Food Bank of Alaska said, “The biggest problem is that the federal government’s programs are dropping as need is growing.”

Ms. Morgan said the decline has affected rural Alaska, where native tribes run most food pantries. She said about 10 percent of the state’s rural food banks have closed because there is not enough federal help coming in.

“They don’t feel staffing and heating is worth it for the small amount of food,” Ms. Morgan said.

Further complicating the picture, Ms. Morgan and others said, is tighter inventory monitoring, which has left many stores with less to donate.

“They know exactly what they have, down to the can,” said Darren Hoffman, a spokesman for the Los Angeles Regional Food Bank, whose supplies are down 11 percent this year. “They can track a lot better and don’t order in bulk. Efficiency has kind of been the enemy of the food bank.”

Extra food — items that are not selling or seasonal inventory that is no longer needed — is now often sold to low-cost retailers, said Tim Viall, executive director of the Greater Stockton Food Bank in Stockton, Calif.

“We’re getting fewer canned goods than last year from retail grocers, because they’re selling it to warehouse food stores,” Mr. Viall said. “We’re putting more reliance on canned food drives, and we’re trying to ramp up the fresh fruit and produce. We are in the heart of one of the most productive agriculture areas in the world, and we’re trying to take advantage.” In places where community donations are down and there are no food manufacturers to solicit, pantries and food banks are making difficult choices. The Society of St. Vincent de Paul food pantry in Cincinnati is giving families less food this year because there is not enough. It has started to ask smaller families to take fewer products.

“Donations are down, and people who need help is up,” said Liz Carter, executive director of the food bank. “So what are we going to do. We just made the decision that instead of giving people six or seven days worth of food, we’re going to give them three or four days of food, which is a drop in the bucket.”