President Obama Warns Don't Celebrate Ending Oil Leak Yet

President Obama called the cap on the gulf oil leak "good news" today, but he cautioned that the job of ending the massive oil leak is not yet complete.

"There were a lot of reports coming out in the media that seemed to indicate, 'Well, maybe this thing is done,'" he said . "We won't be done until we actually know that we've killed the well and that we have a permanent solution in place," he said in the White House Rose Garden before heading off to a Maine vacation.

The president was referring to BP's successful attempt -- so far -- to place a tight cap on the busted oil well and for the first time in 87 days prevent the underwater gusher from pouring into the gulf. BP called Thursday's success a test to see if the device will withstand the pressure of the surging oil, or whether the oil is now leaking out somewhere else in the ocean bedrock.

VIDEO: Oil Shut OffPlay
Gulf Oil Spill: BP Shuts Off Oil Flow

"It's important that we don't get ahead of ourselves here," Obama said today. "You know, one of the problems with having this camera down there is that when the oil stops gushing, everybody feels like we're done. And we're not."

He said the well still has to be permanently plugged and there is the massive clean-up of areas polluted by the spill, which Obama said needs "better coordination on the ground along the shorelines."

"But we are making steady progress," the president said, "and I think the American people should take some heart in the fact that we're making progress on this front."

Scientists today and through the weekend will be combing the area of the leak, looking for evidence of oil seeping through the ocean floor.

VIDEO: For the first time in 87 days, there is no oil leaking into Gulf waters.Play
Gulf Oil Leak Stopped

"It's premature to open the Champagne bottle, but this weekend we'll know whether we contained the monster or not," City University of New York physics professor and SyFy Channel host Michio Kaku told "Good Morning America" today.

There is no sign that the underwater pipe has burst, but scientists are keeping a close eye on the pipe's pressure, currently on the low side at about 7,000 psi, or pounds per square inch.

A sudden drop in pressure, Kaku explained, means the oil has found another way out.

"So far, we don't see that taking place," he said.

The 150,000-pound cap began to successfully contain the leak Thursday afternoon, holding back the oil that's shooting upward with the force of 70 fire hoses.

BP Oil Containment Cap: Video Shows Cap in Test Being Placed on Well

For the time being, work on the relief wells, a mere 100 feet from their target, has been suspended out of fear the drilling could disrupt the pressure to the crippled well.

News of the cap's success met with tepid applause at a Louisiana town hall.

"It's a relief that there's not oil coming into the gulf," shrimper Darla Rocks said, "but not a relief as far as me making a living, not a relief as far as my future."

Retired U.S. Coast Guard Adm. Thad Allen noted that the cap was not a solution, and that work on the leak would continue.

"This is merely an intermediate step to contain the oil, pending finishing the relief wells and plugging the hole," he said.

BP Oil Well, Before and After Flow Stopped

Kaku called the relief wells the "gold standard."

"You choke it from the bottom, cap it from the top," he said.

There were reportedly cheers and slaps on the back in the BP offices as workers realized they'd finally stopped the leak after more than 200 millions of gallons of oil spewed into the ocean. Live video of the leak showed no oil at the site where plumes of oil had been seen billowing into the Gulf since the disaster began April 20.

At the White House, President Obama reacted to the news, saying, "I think it's a positive sign. We're still in the testing phase. I'll have more to say on it tomorrow."

VIDEO: Testing the CapPlay

Louisiana Gov. Bobby Jindal, a Republican, expressed cautious optimism in a statement.

"It is too early to declare victory. ..." Jindal said. "Our battles don't end even when the well is capped. Millions of gallons of oil are still in the Gulf, and some estimates show that oil will continue to hit our shores for many more months or maybe even longer."

Sucess in Stopping Leak Celebrated Cautiously

BP is now conducting step-by-stop tests of the massive, 150,000 pound cap on the wellhead, a process the company said could take up to 48 hours. The company said it is fully possible that oil will escape again before the testing is done.

Engineers slowly ratcheted down the flow of oil this morning and afternoon, closing off three valves -- cutting the so-called kill line at 11:30 a.m. and then closing the choke line at 1:30 p.m., BP executive Kent Wells wrote on the company Twitter account.

Wells called it a "critical milestone," while stressing that it is not an assured success. Oil could flow again, based on the results of well-integrity tests, looking for leaks, that will last anywhere from six to 48 hours.

BP is monitoring pressure readings minute by minute, with higher pressures indicating a successful seal. Low pressures would indicate a leak.

If there is a leak, "they would have to start siphoning [the oil] off again to minimize the leak," Darryl Bourgoyne, the director of LSU's well research lab said today.

ABC News' Russell Goldman, Bradley Blackburn, Ned Potter and Zunaira Zaki contributed to this report.