* Says started buying in March

* Did not tell company he was accumulating stake

* Due to report quarterly holdings Monday night

(Adds quotes)

(Reuters) - Berkshire Hathaway has accumulated a 5.5 percent stake in IBM, Warren Buffett said Monday, his biggest bet on the technology field that he has historically shunned.

Buffett, in a CNBC interview, said he bought about 64 million shares of IBM, which cost around $10.7 billion. Berkshire started buying the shares in March with a goal to build a $10 billion position, he said.

Buffett also said IBM did not know that he was building a stake, and that the company was finding out about his investment for the first time as he said it on CNBC.

The legendary investor said he has always looked at IBM's annual report -- his preferred method of identifying companies to invest in -- but this year, "I read it through a different lens."

Buffett said follow-on conversations with various technology executives throughout the Berkshire conglomerate convinced him to start building the stake.

Berkshire is due to make its quarterly report of its equity holdings on Monday night.

According to Thomson Reuters data, a 5.5 percent position would tie Buffett with State Street Global Advisors for the largest stake in the company.

IBM shares rose nearly 1 percent in premarket trading. Since early March, when Buffett started building his position, IBM shares are up about 17 percent, against a 3 percent decline for the S&P 500. (Reporting by Ben Berkowitz; Editing by Derek Caney, Dave Zimmerman)