President Barack Obama, in his first speech to the nation from the Oval Office, said stopping the worst environmental oil spill in U.S. history has tested the limits of human technology.

Obama spoke Tuesday as he prepared for a Wednesday meeting with BP officials at the White House, calling the Gulf of Mexico disaster “an epidemic” that could take months or years to clean up.

Plans are in place, he said, to cease 90 percent of the oil coming out of the well, leading up to a 100 percent stoppage possibly by the end of summer.

“We’ll use everything we’ve got for as long as it takes,” he said. “Things will never be perfect, and new challenges will always arise … there will be more oil and more damage.”

Obama said he has authorized some 17,000 National Guard troops to aid in the situation. “I urge the governors in the affected states to activate those troops as soon as possible,” he said.

BP will be held accountable for financial and other responsibilities, he said. Also, he said, the time was now, “for this generation,” to explore other energy uses besides those of fossil fuels.

Obama said he had approved expanded offshore drilling a few months ago with the assurances it was absolutely safe. That was not the case aboard the BP rig that exploded, killing 11, he said.

Obama added he wanted to hear a national panel’s recommendations to improve worker safety and environmental protections, and to understand what led to the sinking of the Deepwater Horizon rig.

After the address, Billy Nungesser, president of Plaquemines Parish, La., told CNN the people of Louisiana needed to see “more action on the ground.”

Oval Office speeches are often regarded as historic. Other Oval Office addresses include George W. Bush on the Sept. 11 attacks; George H.W. Bush on Operation Desert Storm; Richard Nixon’s resignation address and Bill Clinton on Somalia.