WASHINGTON » Barely into the new school year, President Barack Obama issued a tough-love message to students and teachers yesterday: Their year in the classroom should be longer, and poorly performing teachers should get out.

American students are falling behind some of their foreign counterparts, especially in math and science, and that’s got to change, Obama said. Seeking to revive a sense of urgency that education reform may have lost amid the recession’s focus on the economy, Obama declared that the future of the country is at stake.

"Whether jobs are created here, high-end jobs that support families and support the future of the American people, is going to depend on whether or not we can do something about these schools," the president said in an interview on NBC’s "Today" show.

U.S. schools through high school offer an average of 180 instruction days per year, according to the Education Commission of the States, compared with an average of 197 days for lower grades and 196 days for upper grades in countries with the best student achievement levels, including Japan, South Korea, Germany and New Zealand.

"That month makes a difference," the president said. "It means that kids are losing a lot of what they learn during the school year during the summer. It’s especially severe for poorer kids who may not see as many books in the house during the summers, aren’t getting as many educational opportunities."

Obama said teachers and their profession should be more highly honored — as in China and some other countries, he said — and he said he wanted to work with the teacher unions. But he also said that unions should not defend a status quo in which one-third of children are dropping out. He challenged them not to be resistant to change.

And the president endorsed the firing of teachers who, once given the chance and the help to improve, are still falling short.

"We have got to identify teachers who are doing well. Teachers who are not doing well, we have got to give them the support and the training to do well. And if some teachers aren’t doing a good job, they’ve got to go," Obama said.

They are goals the president has articulated in the past, but his ability to see them realized is limited. States set the minimum length of school years, and although there is experimentation in some places, there has been no wholesale change since Obama issued the same challenge for more classroom time at the start of the past school year.

One issue is money, and although the president said that lengthening school years would be "money well spent," that does not mean cash-strapped states and districts can afford it.

"It comes down to the old bugaboo, resources. It costs money to keep kids in school," said Mayor Scott Smith of Mesa, Ariz. "Everyone believes we can achieve greater things if we have a longer school year. The question is, How do you pay for it?"

Separately yesterday, Obama announced a goal of recruiting 10,000 teachers over the next two years in the fields of science, technology, engineering and math.