WASHINGTON - Celebrating the ethnic diversity of America, President Barack Obama said more than two dozen foreign-born military members who became US citizens at the White House on the Fourth of July are vivid reminders that welcoming immigrants "is central to our way of life."

He pleaded anew Friday for new immigration policies, saying the vast range of backgrounds and experiences that has made America a melting pot for more than 200 years also makes the country stronger. He argued that the system must be changed for the US to remain the greatest nation on earth.

"The basic idea of welcoming immigrants to our shores is central to our way of life, it is in our DNA,'' Obama said after the 25 service members representing 15 countries raised their right hands and pledged allegiance to the United States.

"From all these different strands, we make something new here in America. And that's why, if we want to keep attracting the best and brightest from beyond our borders, we're going to have to fix our immigration system, which is broken,'' he said.

Deputy Homeland Security Secretary Alejandro Mayorkas, a Cuban who became a naturalized citizen in 1973, administered the oath of allegiance.

The immigration issue is earning renewed attention because of the influx to the US of tens of thousands of unaccompanied children from Central America. Under US law, they must be returned to their home countries, angering immigration advocates who already take issue with Obama's enforcement of deportations. They want Obama to allow the children to stay.

At the same time, Obama blames House Republicans for delaying action on legislation covering the millions already living in the US illegally. A comprehensive measure the Senate passed last summer has been blocked by House leaders who also have done little to advance their own immigration proposals.

Obama announced earlier this week that, as a result of inaction on Capitol Hill, he will pursue non-legislative ways he can adjust US immigration policy on his own. He scheduled a trip to Texas next week, mostly to raise money for Democratic candidates, but plans not to visit the border.

"I'm going to keep doing everything I can to keep making our immigration system smarter and more efficient,'' Obama said Friday.

Across the country, more than 100 demonstrators, most of whom support immigrants, gathered again Friday outside a US Border Patrol station in Murrieta, California, where the agency intends to process some of the immigrants who have flooded the Texas border with Mexico.

Earlier this week a crowd of protesters blocked buses carrying women and children migrants who were flown in from overwhelmed Texas facilities. The Border Patrol had to take the migrants elsewhere.

Later Friday, Obama and his wife, Michelle, welcomed hundreds of military members and their families, including the new citizens, to a barbecue on the South Lawn that was sponsored by the USO, a nonprofit organization that provides services and entertainment to US troops and their families. The event featured a concert by the rapper Pitbull, along with prime seating for the fireworks on the National Mall.

Obama said that since the nation's founding 238 years ago the US has become the "greatest democratic, economic and military force the world has ever known'' and a beacon for others looking on from beyond its borders.

The president explained that he had other reasons to celebrate on Friday.

"This is always a special day for us because this is Malia's birthday,'' he told guests. His oldest child turned 16.