NEW YORK — Concerns over Wall Street practices and economic inequality that have led to sit-ins and rallies in New York and elsewhere reverberated up to the White House today, with President Barack Obama saying the protesters are expressing the frustrations of the American public.

Thousands of protesters, including many in union T-shirts, marched the day before in lower Manhattan, joined by labor leaders who say they will continue to support the protests with manpower and donations of goods and services.

The protests have slowly grown in size and attention over more than two weeks, with the president’s acknowledgment at a news conference a sign they might be jelling into a political movement.

Obama said he understood the public’s concerns about how the nation’s financial system works and said Americans see Wall Street as an example of the financial industry not always following the rules.

“It expresses the frustrations that the American people feel that we had the biggest financial crisis since the Great Depression, huge collateral damage all throughout the country, all across Main Street,” the president said. “And yet you’re still seeing some of the same folks who acted irresponsibly trying to fight efforts to crack down on abusive practices that got us into this problem in the first place.”

He said, though, that the U.S. must have a strong and effective financial sector for the economy to grow, and that the financial regulation bill he championed ensures tougher oversight of the financial industry.

The protesters have varied causes and no apparent demands, but have spoken largely about unemployment and economic inequality, reserving most of their criticism for Wall Street. “We are the 99 percent,” they chanted Wednesday, contrasting themselves with the wealthiest 1 percent of Americans.

“The great thing about Occupy Wall Street is that they have brought the focus of the entire country on the middle class majority,” said George Aldro, 62, a member of Local 2325 of the United Auto Workers, as he carried the union’s blue flag over his shoulder through lower Manhattan.

“We’re in it together, and we’re in it for the long haul.”

Ed Figueroa, a janitor in a public school in the Bronx and a shop steward with Local 32BJ of the Service Employees International Union, said the march was “the first time in these weeks that unions have shown their face.”

“But it won’t be the last time,” he said.

The unions were donating food, blankets and office space to the protesters, said Dan Cantor, head of the Working Families Party. But he said the young protesters would continue to head their own efforts. The movement lacks an identified leader and decisions are made during group meetings.

“They’re giving more to us than we’re giving to them. They’re a shot in the arm to everybody,” Cantor said.

Victor Rivera, a vice president for the powerful 1199 Service Employees International Union, which represents health care workers, said the union had donated “all the food they need for this entire week” to the protesters. Union leaders had also assigned liaisons from their political action committee to work with demonstrators.

“We are here to support this movement against Wall Street’s greed,” he said. “We support the idea that the rich should pay their fair share.”

Late Wednesday, some demonstrators marched toward the New York Stock Exchange but were stopped by police about two blocks away. Police said 23 arrests were made, mostly for disorderly conduct. One person was arrested for assaulting an officer; police said the officer was pushed off his scooter.

Videos show demonstrators clashing with police, screaming expletives and swelling toward uniformed officers, trying to break a police line. A captain in a white shirt swung a baton at the group as several people click photos.

Police spokesman Paul Browne said the line charged at officers after they were told not to do so.

“Those officers have a right to defend themselves,” he said.

No injuries were reported, Browne said. Another officer used pepper spray under similar circumstances, Browne said. According to the patrol guide, officers are allowed to use such instruments in order to defend themselves.

The Occupy Wall Street protests started Sept. 17 with a few dozen demonstrators who tried to pitch tents in front of the New York Stock Exchange. Since then, hundreds have set up camp nearby in Zuccotti Park and have become increasingly organized, lining up medical aid and legal help and printing their own newspaper.

On Saturday, about 700 people were arrested and given disorderly conduct summonses for spilling into the roadway of the Brooklyn Bridge despite warnings from police. A group of those arrested filed a lawsuit Tuesday, saying officers lured them into a trap before arresting them. Video shows officers using bullhorns to try and tell the group to get off the road.

Several Democratic lawmakers have expressed support for the protesters, but some Republican presidential candidates have rebuked them. Herman Cain called the activists “un-American” Wednesday at a book signing in St. Petersburg, Fla.

“They’re basically saying that somehow the government is supposed to take from those that have succeeded and give to those who want to protest,” the former pizza-company executive said. “That’s not the way America was built.”

On Tuesday, CBS reported that former Massachusetts Gov. Mitt Romney called the protest “class warfare” at an appearance at a Florida retirement community.

Activists have been showing solidarity with the movement in many cities, including Los Angeles, Boston, Seattle and Providence, R.I.

Many of those protesting are college students. Hundreds walked out of classes in New York, some in a show of solidarity for the Wall Street movement but many more concerned with worries closer to home. Protests were scheduled at State University of New York campuses including Albany, Buffalo, Binghamton, New Paltz and Purchase.

Danielle Kingsbury, a 21-year-old senior from New Paltz, said she walked out of an American literature class to show support for some of her professors who she said have had their workloads increased because of budget cuts.

“The state of education in our country is ridiculous,” said Kingsbury, who plans to teach. “The state doesn’t care about it and we need to fight back about that.”