Nov. 13 (Bloomberg) -- Goldman Sachs Group Inc., the biggest U.S. securities firm by market value, doesn't plan to take significant writedowns on mortgage-related assets, Chief Executive Officer Lloyd Blankfein said today.

Goldman rose 8.5 percent in New York Stock Exchange composite trading, the biggest gain in 6 1/2 years, after Blankfein made the comment at a conference in New York hosted by Merrill Lynch & Co. He also said the firm is still betting that mortgage-backed securities and collateralized debt obligations will drop.

``The spreads in these markets have continued to widen out'' since the third quarter, Blankfein, 53, said in response to a question about the firm's position. ``Given that point of view, we continue to be net short in these markets.''

Goldman shares climbed $18.33 to $233.04 at 4:43 p.m. in New York. They've gained 17 percent this year. The company is on pace to post its fourth consecutive record annual profit, even as other brokerages and banks, including Merrill Lynch and Citigroup Inc., have written down their mortgage-related assets by more than $45 billion.

Guy Moszkowski, the Merrill Lynch analyst who follows securities firms, asked Blankfein at the conference about speculation that Goldman may post a loss on mortgage-backed investments.

``Are you thinking that you will, or planning to take, a significant writedown?'' Moszkowski asked.

``No,'' Blankfein replied.

Goldman has ``a pretty good grip'' on the valuation of its so-called Level 3 assets, which are the most difficult to value, Blankfein said. Assets that fall into the category include mortgage-related securities and loans for leveraged buyouts, as well as private equity and real estate investments.

To contact the reporter on this story: Christine Harper in New York at charper@bloomberg.net.

Last Updated: November 13, 2007 17:05 EST