UPDATE 3-CRH to seek more cost cuts after H1 profit plunge

* Says H1 pretax drops by estimated 83 percent

* Rate of profit decline will ease in H2 vs H1

* Total annualised savings of 1.45 bln euros in 2007-2010

* Sees more acquisition opportunities

* Stock up over 6 pct, outpacing 3 pct bourse gain

(Adds fund manager comment, updates shares)

By Carmel Crimmins

DUBLIN, July 7 (Reuters) - Building materials group CRH Plc (CRH.I)(CRH.L) warned pretax profit nosedived in the first half and said trading would remain extremely difficult, but investors bet the worst was behind the Irish group, sending its shares sharply up.

Ireland's largest listed company by stock market value said it would ramp up cost-cutting in response to an estimated 83 percent slide in pretax profit in January through June and tough conditions ahead.

CRH, one of the world's biggest suppliers of asphalt, paving slabs, bricks and other construction products, said it was targeting an additional 555 million euros in annualised cost savings for 2009 and 2010, on top of 895 million announced in January, with layoffs and plant closures in the frame.

It did not say how many jobs would go. The company employs 93,500 worldwide, according to its website.

Shares in the group, which dominates the Irish index .ISEQ, were up over 6 percent at 16.2 euros at 1345 GMT, reversing Monday's 5 percent drop and an initial fall of around 4 percent in early trade.

"It's an earnings recovery play," said one Dublin-based dealer. "Our view is that all of the surprise will be on the upside, because you have slashed the cost base and earnings estimates have been realigned to a fairly low expectation."

But not everyone was convinced the bottom had been hit.

"The trouble is, every time the numbers get worse, people say this is the trough," said Reg Watson, investment director at Standard Life Investments.

"They have managed to pull a rabbit out of the hat by cost-cutting internally. But if you want to be cynical about it, the question is why they haven't been able to achieve these cost savings sooner?" Watson said.