President Obama said Tuesday that now is a good time for investors to buy stocks if they focus on the big picture.

The Dow plunged Monday to its lowest level in 12 years. 

"What you're now seeing is a profit and earnings ratios get to the point that buying stocks is a good thing if you have a long-term perspective on it," he said to reporters after meeting in the Oval Office with visiting British Prime Minister Gordon Brown.

The president compared the market to daily tracking polls used by politicians, saying that paying too close attention to Wall Street's "fits and starts" could lead to bad long-term policy. 

"The stock market is story of like a tracking poll in politics. It bobs up and down day-to-day," Obama said. "And if you spend all your time worrying about that, then you're probably going to get the long-term strategy wrong."

Obama said he is not measuring policies against "the day-to-day gyrations of the stock market," but by whether lending is flowing more freely, businesses are investing and the unemployed are going back to work.

He said he is "absolutely confident" that those things will happen. But the president also said it will take time fore the mistakes of the past to work their way through the system. 

"There are a lot of losses that are working their way through the system and it's not surprising the market is hurting as a consequence," he said. "We dug a very deep hole for ourselves. There were a lot of bad decisions that were made. We are cleaning up that mess. It's going to be sort of full of fits and starts, in terms of getting the mess cleaned up, but it's going to get cleaned up. And we are going to recover, and we are going to emerge more prosperous, more unified, and I think more protected from systemic risk."

The Associated Press contributed to this report.