By Deborah Levine, MarketWatch NEW YORK (MarketWatch) -- Treasury prices turned higher on Wednesday, pushing yields down for a fourth session, after rating agencies turned more sour on sovereign debt, adding to concerns about future credit problems and reviving interest in the relative safety of U.S. debt. Gains may be limited before the government sells $21 billion in 10-year notes, the second of three auctions this week. Yields on 2-year notes (UST2YR 0.71, 0.00, -0.56%) slipped 1 basis point to 0.72%. A basis point is 0.01% and yields move in the opposite direction as prices. Ten-year note yields (UST10Y 3.38, -0.01, -0.18%) were little changed at 3.38%, after being higher before the rating agencies' releases. Standard & Poor's lowered its outlook on Spain's debt. Also, Moody's Investors Service said it may lower its rating on government-related issuers in the United Arab Emirates, continuing the saga related to Dubai World's debt problems in the last week. See more on Dubai. Still, traders were concerned the Treasury Department wouldn't see the type of demand from investors that the 3-year note sale (UST3YR 1.21, 0.00, 0.00%) received Tuesday. "Without any pressing economic data today the focus will be about supply of 10's and 30's," Thomas di Galoma, head of fixed income rates trading at Guggenheim Partners, wrote in an email. The Treasury Department will close the auction at 1 p.m. Eastern time. The sale is a reopening, meaning the debt to be sold will carry the same coupon and maturity as the original issue sold last month. The amount is $1 billion bigger than the last reopening of 10-year notes. At the last four reopenings of 10-year debt, bidders offered an average of 2.92 times the amount of debt being sold, according to RBS Securities. Indirect bidders, a group of investors that includes foreign central banks, purchased an average of 45.2% of the sales. The government will also sell $13 billion in 30-year bonds (UST30Y 4.36, -0.01, -0.30%) on Thursday, which is also a reopening.

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