* Retail sales down for 3 straight months
* Gains best in long maturities
* Traders readying for long bond auction
By Michael Connor
NEW YORK, March 12 (Reuters) - U.S. Treasury debt prices rose for a fourth day on Thursday, with gains accelerating after the government reported unexpectedly soft U.S. retail sales during February.
The 30-year Treasury, which this week has benefited most from relative-value investment flows caused by Europe's massive bond-buying program, was last up 19/32 and yielding 2.6534 percent after touching a low of 2.634 percent.
The Commerce Department reported shortly after the start of New York trading that U.S. retail sales had unexpectedly fallen for a third straight month in February.
Retail sales dropped 0.6 percent last month, after declining 0.8 percent in January, and were slowed by harsh weather in much of the country. It was the first time since 2012 that sales had dropped for three consecutive months.
"There's been good buying since we got very, very disappointing retail sales," said Justin Lederer, an analyst at Cantor Fitzgerald in New York.
The persistent weakness in retail sales stoked speculation over the timing of interest rate hikes by Federal Reserve policymakers. They meet next week and may move towards ending an era of near-zero U.S. rates by removing the word "patient" from a post-meeting comment.
"Today is not necessarily a game changer for the Fed. I think they take out 'patient' next week and we are still looking at mid-2015 liftoff," Lederer said. "But if we keep getting weak data prints, we could get delays in liftoff."
Other longer maturity Treasuries also put up the session's bigger price gains, with the benchmark 10-year last up 8/32 and yielding 2.084 percent, according to Thomson Reuters data.
Three-year and other shorter maturities most affected by changes in Fed interest-rate policies were up more modestly on Thursday, as they have been all week.
Since Monday, when the European Central Bank began a 1.1 trillion euro bond-buying program to battle economic sluggishness, Treasuries have been rallying as foreign investors scoop up much higher-yielding U.S. debt securities.
European bond yields have plumbed record lows this week. The 10-year German bund last yielded 0.237 percent, or about 184 basis points under the 10-year Treasury.
Traders were also readying for a Treasury Department auction later on Thursday of $13 billion of 30-year bonds that comes after other debt sales this week, including a $21 billion sale of 10-year notes that was heavily bid by foreigners.
"With 30-year yields well off of the record lows the interest rate differential vs the rest of the world should contribute to strong overseas demand," CRT Capital strategist Ian Lyngen told clients.
Reporting By Michael Connor in New York; Editing by Meredith Mazzilli