JGBs dip on economic optimism, 40-yr auction eyed

* Superlong bonds slip before Thursday's 40-year auction

* June futures match April low of 136.43

TOKYO, May 13 - Japanese government bonds dipped on Wednesday as some investors trimmed their holdings of safe-haven government debt on optimism the worst of the global economic slump is over.

Dealers hedging against the Ministry of Finance's 40-year JGB auction on Thursday also helped push down bonds with a maturity greater than 10 years.

But activity was subdued as most market participants remain unconvinced the global economy is about to make a vigorous recovery.

"It usually takes about three months to figure out whether the economy is heading towards a strong recovery after signs that it has hit bottom start to emerge," said Mari Iwashita, chief market economist at Daiwa Securities SMBC.

June 10-year JGB futures slipped 0.27 point to 136.47 after falling to match April's low of 136.43. A slide below that level would take the lead futures contract to its lowest since late October.

Traders said short-term speculators might be selling futures on an opinion story in the Financial Times that touched on the risk of the United States losing its triple A credit rating and refocused attention on rising U.S. debt issuance.

"The cash bond market showed muted reaction to the opinion piece as the risk of Treasuries having their rating downgraded is nothing new," said a bond trader at a Japanese brokerage.

The yield of the new benchmark No.300 10-year JGB rose 1 basis point to 1.445 percent.

The benchmark 10-year yield has traded in a 1.395-1.490 percent range for just over a month. Analysts and traders said this was likely to last for another month as investors are not likely to get firm evidence the Japanese economy is on a sustainable recovery path in near term.

At the same time, JGBs will draw support from expectations it will take some time before the Bank of Japan starts to raise interest rates from the current 0.1 percent.

The two-year yield was unchanged on the day at 0.385 percent, while the five-year yield rose 1.5 basis points to 0.855 percent.

The 20-year yield inched up 1 basis point to 2.080 percent.