WASHINGTON — The Senate threw its support behind the potato Tuesday, voting to block an Obama administration proposal to limit the vegetable on school lunch lines.

Agriculture Department rules proposed earlier this year aimed to reduce the amount of french fries in schools, limiting lunchrooms to two servings a week of potatoes and other starchy vegetables. That angered the potato industry and members of Congress from potato-growing states, who say USDA should focus on the preparation instead and that potatoes can be a good source of fiber and potassium.

Following a bipartisan agreement on the issue, the Senate by voice vote accepted an amendment by Republican Sen. Susan Collins that would block USDA from putting any limits on serving potatoes or other vegetables in school lunches.

Collins, who is from Maine, a potato-growing state, says the vegetables are a cheaper and nutritious way to feed children when school budgets are strapped.

"This proposed rule would have imposed significant and needless costs on our nation's school districts at a time when they can least afford it," she said.

Amended was a spending bill that includes dollars for the Agriculture Department. The House passed a similar bill earlier this year including language that would ask the department to rewrite its school lunch rules entirely. Republicans have singled out the potato proposal in criticizing the rules, saying the government shouldn't be dictating what kids can eat.

Advocates and government officials say children get enough potatoes already and should have more diversity in their diets

"USDA's proposal was about helping kids to eat a very wide variety of vegetables and I think that point has been lost in all this," said Margo Wootan, director of nutrition policy at the advocacy group Center for Science in the Public Interest, which pushed for the standards. "Other vegetables have a hard time competing with potatoes."

Since the guidelines apply to federally subsidized meals, schools are generally fine with broad federal guidelines on nutrition — how many servings a week children are allowed of grains or vegetables, for example. But some schools have balked at the attempt to tell them exactly what foods they can't serve.

Many critics said the proposal ignores schools that have long since taken the "fry" out of french fry. Though they may be fried as part of initial processing, schools are now preparing them with little grease and no crispiness, serving them to kids as a healthier option.

The way the amendment is worded — blocking the department from limiting potatoes — would still give USDA flexibility to regulate the preparation of the potatoes when it issues the final version of the school lunch rule.

""This amendment seeks to ensure flexibility for schools to provide nutritious and affordable school meals," said Democratic Sen. Mark Udall of Colorado, another potato-growing state. Udall co-sponsored the amendment with Collins.