U.S. and Japan drive G7 recovery as euro zone lags - OECD

* Economic growth rebounding in U.S. and Japan

* Growth trends diverging in the euro zone

* ECB urged to cut rates, Japan easing welcomed

PARIS, March 28 (Reuters) - The United States and Japan are leading a rebound in advanced economies while the still fragile euro zone needs an interest rate cut to ensure a recovery takes hold, the OECD said on Thursday.

The outlook has finally strengthened for the Group of Seven economies, though it is still too soon for governments and central banks to drop exceptional measures to prop up growth, the Organisation for Economic Co-operation and Development said.

The OECD forecast that these major economies would grow on average 2.4 percent in the first quarter on an annualised basis, after shrinking 0.5 percent in the previous three months.

Their growth pace would cool slightly in the second quarter to average 1.8 percent in the second quarter, the Paris-based organisation forecasts.

"The bottom line is that we are moderately more optimistic," OECD chief economist Pier Carlo Padoan told Reuters. "We see growth firming in the U.S., we see more growth in Japan thanks to new measures, and we see more growth in Germany."

The OECD's latest predictions were contained in a brief report in which it gives quarterly estimates for a handful of countries before a fuller publication in May.

The United States, the world's biggest economy, was seen leading the pack with growth estimated to reach 3.5 percent in the first quarter, slowing to 2.0 percent in the following three months.

New measures to boost the Japanese economy would help it grow 3.2 percent in the first quarter and 2.2 percent in the second quarter.

DIVERGING FORTUNES

However, growth rates diverged widely among the euro zone's biggest economies with Germany seen bouncing back after shrinking at the end of 2012 to grow 2.3 percent in the first quarter and 2.6 percent in the second quarter.

In contrast, France was seen emerging from recession only in the second quarter, with growth of 0.5 percent, while Italy would remain stuck in a long-running recession.

With inflation low, Padoan said the European Central Bank would be justified in cutting interest rates and an explicit indication of its future intentions for rates could be needed.

While plans in Japan for more aggressive central bank easing were also welcome in the OECD's eyes, it said the need for such measures in the United States was beginning to subside.

"In the United States the benefits of further QE (quantitative easing) might be declining while the costs of further QE might be rising," Padoan said.

The OECD warned that vast amounts of central bank liquidity pumped into economies may be encouraging some investors to take on too much risk given the still shaky foundations of recovery in most economies.

"We see a lot of risk taking showing up in a number of asset markets because of abundant liquidity seeking yield," Padoan said, citing in particular the corporate bond market.

(Reporting by Leigh Thomas; Editing by Ruth Pitchford)