Warren Buffett said Wednesday the threat to not raise the nation's debt limit "after you've already spent the money" is a "political weapon of mass destruction" comparable to poison gas and shouldn't be used by either party. "I know it's been used in the past, but we used the atomic bomb back in 1945 but we decided we weren't going to do something like that again," he said hours before the government's midnight deadline to raise the debt limit or possibly default.

Buffett called on both sides to pledge not to use the debt limit as a weapon. "There are plenty of weapons that can be used," like filibusters, he said. In a live interview on CNBC's "Squawk Box, the Berkshire Hathaway chairman said he doesn't expect the U.S. will do anything to damage its 237-year reputation of paying its bills on time, but if it does it would be a "pure act of idiocy" and "asinine." "Credit worthiness is like virginity, it can be preserved but not restored very easily, so it is crazy to play around with it," he said. Buffett said Berkshire owns short-term Treasury securities but he isn't worried about getting paid.

He also said the ongoing crisis in Washington over spending and the debt limit is no reason to avoid buying securities, pointing out that Berkshire subsidiary Marmon Group just paid $1.1 billion for a British drinks dispensing business. "We did not buy it with a condition that we could call off the deal" if there was no vote to raise the debt limit, he said.

He added that in his long career, he has never put off a deal by a few weeks to see what might happen in Washington. (Read more: Berkshire Hathaway's 15 Biggest Stock Holdings)

When it was pointed out to him that he may be "unique" because he is a long-term investor, he replied that "most people are." "If you take the people I meet in Omaha, you take the people who own farms, you take the people who own apartment houses, most people are long-term investors, thank heavens," he said.

Buffett rejected the idea that investors should be worried about a bull market "bubble" for stocks. He said, "We could at some point, but no, stocks are not selling at bubble levels. What do you diversify in? You want to diversify into cash? I think it's a terrible investment compared to equities. You want to diversify into long-term bonds? I think it's a terrible investment compared to equities." Buffett also said Berkshire's spending rate on acquisitions this year is as "high as ever." He told Becky Quick he had been working on a big acquisition, a $12 billion "elephant," but the deal didn't come together. Buffett was interviewed in Washington where he is attending Fortune's Most Powerful Women summit.



Moments after Bank of America announced better than expected earnings, Buffett said "the banks are in the best shape I can remember." He also defended JPMorgan Chase CEO Jamie DImon amid the bank's many legal problems, some of which are the result of its acquisition of Washington Mutual at the height of the financial crisis in 2008. "If a cop follows you for 500 miles, you're going to get a ticket. And believe me, you've had a lot of cops" following JPMorgan, he said. (Read more: Buffett on JPMorgan: Jamie Dimon will survive fine)

Responding to activist investor Carl Icahn's public calls for a large Apple stock buyback, Buffett said, "I think Apple's management has done a pretty good job of running the company... and my vote would be with them." He joked, "I just wish I'd bought the stock many years ago."

"I do not think companies should be run primarily to please Wall Street and largely shareholders who are going to sell. I believe in running Berkshire for the shareholders who are going to stay and not for the ones who are going to leave," he added.

Buffett said he has a "rooting interest" for the troubled retailer J.C. Penney because he worked in one of their stores when he was younger, but acknowledged it's "very, very tough" to compete against competitors who are always moving. "Coming from behind in retailing is just plain tough," he said. Berkshire companies are still selling a "significant" amount of goods to Penney under "normal terms," he said and he's not worried about the retailer's survival. In response to a question about the Obamacare health exchange rollout, Buffett said with a chuckle that he's glad he wasn't in charge, but argued that something is going to have to be done to control medical costs. They are the "tapeworm" of the American economy, he said. On the economy, Buffett said he continues to see slow improvement and pointed out that "two percent a year growth with less than one percent population gains means one percent real growth per capita. In 20 years that's 20 percent. If every generation lives 20 percent better than the generation before them, that's not terrible."