UPDATE 1-NZ's Contact Energy sees lower earnings in current yr

* After-tax earnings up to 33 pct lower in current year

* Full hydro lakes send wholesale power prices tumbling

WELLINGTON, June 8 (Reuters) - New Zealand's biggest listed energy company Contact Energy Ltd (CEN.NZ) said on Monday that it expected to see its underlying earnings fall by as much as 33 percent because of lower wholesale electricity prices.

It said full hydro lakes have resulted in low prices and less likelihood of the need for more expensive thermal generation, which is a significant part of the company's generation capacity.

"The recent high inflows have resulted in the outlook for wholesale prices remaining low for the rest of the year," chief executive David Baldwin said in a statement.

In the year to June 2008, underlying earnings after tax were NZ$232.8 million ($146 million).

Shares in Contact, a top-10 company, closed on Friday at NZ$5.80, and have fallen 22 percent so far this year, compared with a 4.4 percent gain in the benchmark top 50 .NZ50 index.

At its half-year result in February, Contact reported a 79 percent fall in net-profit due to a mix of higher costs and lower generation.

Storage in the South Island's hydro lakes is about 136 percent of average, Contact said, and the oversupply has been exacerbated by unscheduled outages at the country's largest single consumer, the Rio Tinto-owned (RIO.AX) aluminium smelter at Tiwai Point.