UPDATE 2-Berkshire boosts ConocoPhillips stake, buys Eaton

* Nearly quintuples ConocoPhillips stake

* Buys shares of diversified manufacturer Eaton

* Purchases come as Buffett buys stocks for own portfolio (Adds comments, details of other holdings, background)

By Jonathan Stempel

NEW YORK, Nov 14 (Reuters) - Billionaire Warren Buffett's Berkshire Hathaway Inc (BRKa.N) (BRKb.N) said on Friday it has nearly quintupled its holdings in oil company ConocoPhillips (COP.N), and taken a new stake in hydraulics manufacturer Eaton Corp (ETN.N).

Berkshire disclosed its investments in a U.S. Securities and Exchange Commission filing, in which it reported holdings of stocks on U.S. exchanges as of Sept. 30.

The Omaha, Nebraska-based insurance and investment company said it owned 83.96 million shares in Houston-based Conoco, worth $6.15 billion, as of the end of September, equal to a 5.6 percent stake. That is up from 59.69 million shares as of June 30, and 17.51 million three months earlier.

Buffett had previously kept the June stake confidential. The SEC often lets Buffett, one of the world's richest people and perhaps its most revered investor, delay disclosure of his investing activity so others cannot copy him.

Conoco was Berkshire's fourth-largest U.S. stock investment as of Sept 30, after Wells Fargo & Co (WFC.N), Coca-Cola Co (KO.N) and Procter & Gamble Co (PG.N).

Earlier this decade, Berkshire reaped a large profit from investing in Chinese oil company PetroChina Co (601857.SS).

"Energy companies are trading at massive discounts," said Mohnish Pabrai, managing partner at Pabrai Investment Funds in Irvine, California, which owns Berkshire shares. "Oil prices have come down, but many of these companies are extremely profitable even with oil at $60 a barrel. Buffett has invested before in PetroChina, so he understands the business."

Berkshire also said it has bought 2.91 million shares of Cleveland-based Eaton, worth $163.4 million as of Sept 30. Eaton's products include industrial automation technology and hydraulics used in airplanes and truck drive-train systems.

Berkshire, Conoco and Eaton did not immediately return calls seeking comment.

Conoco shares rose 2.4 percent after-hours after Berkshire revealed its stake. Trades were not available for Eaton.

Buffett last month expressed confidence in corporate America by saying he will move all his personal holdings, apart from Berkshire shares, to U.S. stocks from government bonds.

"Be greedy when others are fearful," he wrote in the New York Times.

BUFFETT BUYS IN TOUGH ENVIRONMENT

The disclosure of Berkshire's holdings provides insight on where Buffett is finding value in a difficult year for stocks.

He tends to favor blue-chip companies with market-leading positions, easy-to-follow businesses and strong management.

The report does not include preferred stock investments in Goldman Sachs Group Inc (GS.N) and in General Electric Co (GE.N) that Berkshire revealed in the last two months.

Berkshire's stock holdings on U.S. exchanges totaled $69.89 billion. Its overall equity holdings, including on non-U.S. exchanges, rose 9 percent over that time to $76.04 billion. Berkshire bought about $3.9 billion of stock in the quarter.

Pabrai said Berkshire's trading activity in the fourth quarter will be particularly noteworthy, given the plunge in stock markets worldwide. "We are seeing valuations now that we haven't seen in several decades," he said. "I would expect quite a bit of movement from Berkshire in the fourth quarter."

In Friday's filing, Berkshire also revealed increased stakes in NRG Energy Inc (NRG.N) and U.S. Bancorp (USB.N), a small sale of Wells Fargo stock, and reduced stakes in Bank of America Corp (BAC.N), used car retailer CarMax Inc (KMX.N), home improvement companies Home Depot Inc (HD.N) and Lowe's Companies (LOW.N), and health insurer WellPoint Inc (WLP.N).

Buffett has transformed Berkshire since 1965 into a $156 billion conglomerate with at least 76 companies selling such things as insurance, candy, ice cream, knives and underwear.

In Friday trading, Berkshire Class A shares closed down $1,800 at $101,000. Its Class B shares fell $36 to $3,389. (Reporting by Jonathan Stempel; Additional reporting by Anna Driver in Houston, editing by Matthew Lewis and Tim Dobbyn)