TOKYO, April 30 (Reuters) - Japanese government bond prices mostly slipped on Tuesday, as investors made room in their portfolios to buy at the next day's 10-year sale. * The Ministry of Finance will offer 2.4 trillion yen ($24.45 billion) of 10-year notes. * "The sale is expected to be uneventful. I don't hear anyone expressing any worry about it," said a fixed income fund manager at a Japanese asset management firm in Tokyo. "This trading week is short because of Golden Week, so supply and demand factors will be driving the market," he added. * Tokyo markets were closed on April 29, and will also be shut for holidays on May 3 and May 6. The string of holidays is known as Golden Week. * The Bank of Japan on Tuesday offered to buy JGBs outright in its regular asset-purchasing operations. The central bank said it will buy up to 200 billion yen of notes with residual maturities of more than 1 year and up to 3 years, and an additional 400 billion yen of notes with residual maturities of more than 3 year and up to 5 years. It also offered to buy 140 billion yen in floating-rate JGBs. * The 10-year yield added 1 basis point to 0.600 percent, up from 0.580 percent earlier in the session but within last week's trading range of 0.575 to 0.610 percent. * Ten-year futures finished morning trade down 0.13 point at 144.52, after rising as high as 144.79. * The 20-year JGB yield was flat at 1.475 percent and the 30-year bond was so far untraded, its yield closing last Friday at 1.600 percent. * Market participants largely shrugged off government data released early on Tuesday that showed Japanese household spending rose a greater-than-forecast 5.2 percent in March from a year earlier in price-adjusted real terms.