Becky Domokos-Bays of Alexandria City Public Schools has served her students whole-grain pasta 20 times. Each time, she said, they rejected it.

Starting next school year, pasta and other grain products in schools will have to be whole-grain rich, or more than half whole grain. That includes rolls, biscuits, pizza crust, tortillas and even grits.

The requirement is part of a government effort to make school lunches and breakfasts healthier. Championed by first lady Michelle Obama, the new standards have been phased in over the last two school years, with more changes coming in 2014.

Some schools say the changes have been expensive and difficult to put in place, and school officials are asking Congress and the Agriculture Department to roll back some of the requirements. Their main concerns: finding enough whole grain-rich foods that kids like, lowering sodium levels and keeping fruits and vegetables from ending up in the trash.

In interviews, school nutrition directors across the country mostly agreed that healthy changes were needed in school lunches -- long famous for daily servings of greasy fries and pizza. Kids have adapted easily to many of the changes, are getting more variety in the lunch line and are eating healthier.

But Domokos-Bays and other school nutrition directors say the standards were put in place too quickly as kids get used to new tastes and school lunch vendors rush to reformulate their foods. When kids don't buy lunch, or throw it away, it costs the schools precious dollars.

"The regulations are so prescriptive, so it's difficult to manage not only the nutrition side of your businesses but the business side of your business," Domokos-Bays said.

Some of the main challenges reported by school nutrition directors:

--Whole grains. While many kids have adapted to whole grain rolls, breads and even pizza crusts, some schools are having problems with whole grain-rich pastas, which can cook differently. USDA's Janey Thornton, a former school nutrition director, says the government is working with the food industry to develop better pastas.

Whole grains have also proved a hard sell for some popular regional items, like biscuits and grits in the South. Lyman Graham of the Roswell, New Mexico, school district says tortillas are one of the most popular foods in his area, but the whole wheat flour versions are "going in the trash."

--Sodium. Schools will have to lower the total sodium levels in school meals next school year and then will have to lower them even further by 2017.

School lunch directors say the 2017 target -- 640 milligrams total in an elementary school lunch and 740 milligrams in a high school lunch -- isn't feasible and say kids will reject the foods. USDA's Thornton acknowledges the food industry isn't there yet but encourages frustrated school lunch directors to "worry about today first before we imagine the worst down the road."

--Fruits and vegetables. The standards require every student to take a fruit or vegetable to create a balanced plate. The reaction among students has been mixed. "If the kids don't eat the food, then all I have is healthy trash cans," said Peggy Lawrence, director of nutrition at the Rockdale County Public Schools in Georgia.

--Healthier snacks. Schools will for the first time this year have to make sure that all foods, including vending machines and a la carte lines, meet healthier standards. While many schools have already moved to make snacks healthier, others depend on snack money to help operate their lunchrooms and are worried about a sales dip.

The School Nutrition Association has asked Congress and USDA to only require that 50 percent of foods be whole grain-rich, to suspend the 2017 sodium requirements and to stop requiring students to take a fruit or vegetable.

Margo Wootan, a nutrition lobbyist for the Center for Science in the Public Interest who has pushed for healthier meals, says relaxing those standards could gut the program. "You can't call a meal a meal without a fruit or vegetable," she said.

USDA has shown some flexibility already: In 2012, the department scrapped maximums on proteins and grains after students complained they were hungry.

USDA's Thornton says problems will lessen as the food industry creates healthier products. "I'll bet that five or seven years down the road, we'll see kids eating healthy food and we'll see acceptance," she said.

Republicans say they may intervene before then. Alabama Rep. Robert Aderholt, the Republican in charge of the House spending committee overseeing USDA, has said school districts need a "pause" while problems are worked out.

Aderholt's panel is expected to release a new spending bill this month that may propose changes. Republicans also are eying the next five-year renewal of the school foods policy, due in 2015.

Sam Kass, senior policy adviser for nutrition at the White House, said last month that there have been "tremendous gains" in school foods and said he finds efforts to undermine that disappointing. "First and foremost, the key is not going back," he said.

At Alexandria's Patrick Henry Elementary last Tuesday, students said they loved their lunches and gobbled up plump strawberries. Kindergartner Jade Kennedy said she recently tried kiwi at school for the first time.

But Domokos-Bays said she will serve white pasta to the students until she has to make the change this summer. Tuesday was pasta day, and several children said it was their favorite lunch -- "better than my mom made," first-grader Ruth Gebregiorgis said.