TREASURIES-US bonds mostly climb on Fed's bond-buy program

*Bonds mostly rise on Fed's Treasury buying program

*Gains follow Wednesday's yield drop of nearly 50 bps

*Jobless claims data adds to bullish tone (Adds Philly Fed index in final paragraph, updates prices)

By Chris Reese

NEW YORK, March 19 (Reuters) - U.S. Treasuries mostly rose on Thursday as the market was still grasping the impact of Wednesday's Federal Reserve's plan to buy long-term Treasuries, which prompted the biggest single-day drop in benchmark yields since 1987.

The Fed said on Wednesday it would buy up to $300 billion of longer-dated Treasuries over the next six months in an attempt to boost the economy, and the benchmark yield promptly shed nearly 50 basis points.

"We are still feeling the after-effects of that," said Kim Rupert, managing director of global fixed income analysis at Action Economics LLC in San Francisco, adding "Treasuries still have a solid bid at these new, higher (price) levels."

The benchmark 10-year Treasury note US10YT=RR was trading 8/32 higher in price for a yield of 2.52 percent, down from 2.55 percent late on Wednesday, while the two-year note US2YT=RR was unchanged in price for a yield of 0.84 percent.

Adding to the bullish tone in Treasuries on Thursday was U.S. data showing that the four-week average of claims for jobless benefits rose to the highest since October, 1982, indicating the jobs market remains in a dire condition.

"There is no sign of even a temporary easing in the downward pressure on employment," said Ian Shepherdson, chief U.S. economist at High Frequency Economics in Valhalla, New York.

Five-year Treasury notes US5YT=RR were trading 4/32 higher in price for a yield of 1.55 percent, down from 1.58 percent late on Wednesday, while the 30-year bond US30YT=RR was 18/32 lower in price for a yield of 3.57 percent from 3.54 percent.

The New York Fed said on Wednesday that Treasury purchases will focus on a range between two-year to 10-year securities, and the 30-year bond has not seen the sharp price benefits from the Fed announcement that has undercut benchmark yields.

The yield curve, or the spread between yield on two-year notes and 10-year notes, was its flattest Jan. 20, narrowing to 168 basis points.

The bond market showed no noticeable impact from data on factory showing activity in the U.S. Mid-Atlantic region shrank less severely in March than in February. The Philadelphia Fed said on Thursday that its business activity index was minus 35.0 from minus 41.3 in February. A reading below zero indicates contraction in the region's manufacturing sector. (Reporting by Chris Reese; Editing by Walker Simon)