UPDATE 3-Buffett's Berkshire has first loss since 2001

* ConocoPhillips, derivatives hurt results

* Economy weighs on several businesses

* Insurance units post better results (Adds investor comment, more details on Berkshire businesses)

By Jonathan Stempel

NEW YORK, May 8 (Reuters) - Warren Buffett's Berkshire Hathaway Inc (BRKa.N) (BRKb.N) posted its first quarterly loss since 2001, hurt by losses on derivative contracts, a big investment in the oil company ConocoPhillips (COP.N), and the weakening economy.

The net loss for the Omaha, Nebraska-based insurance and investment company was $1.53 billion, or $990 per Class A share, and compared with a profit of $940 million, or $607, a year earlier.

Excluding investments, operating profit fell 12 percent to $1.71 billion, or $1,100 per share, from $1.93 billion, or $1,247. That profit was in line with the $1.7 billion that Buffett estimated at Berkshire's annual meeting last Saturday.

Analysts on average expected operating profit of $1,087 per share, according to Reuters Estimates. Revenue fell 9.5 percent to $22.78 billion. Book value per Class A share fell 6.1 percent to $66,248, following a 9.6 percent drop in 2008.

Buffett said many of Berkshire's nearly 80 businesses were hurt by the recession and lower consumer spending, including housing-related units that make bricks, insulation and paint.