UPDATE 2-ASML cuts first-half sales forecast on weaker Q2

* Sees H1 sales of 3 bln euros including EUV sales

* Previously saw 3 bln euros of sales excluding EUV

* Blames slower Q2 demand from logic customers

(Adds analyst comment)

AMSTERDAM, April 16 (Reuters) - ASML, the world's biggest manufacturer of tools for semiconductor chip makers, cut its first-half sales forecast on Wednesday, blaming slower second-quarter sales to some customers.

The Dutch firm said it now expected sales of 3 billion euros ($4.2 billion) in the first half of its fiscal year, including sales of extreme ultraviolet (EUV) systems. Previously it had forecast sales of 3 billion excluding EUV systems.

"Sales in the second quarter are ... expected to be affected by adjustments of system demand from some logic customers," it said in its earnings statement.

ASML supplies most of the world's major chip manufacturers, including Samsung Electronics Co. Ltd, Intel Corp and Taiwan Semiconductor Manufacturing Co Ltd (TSMC) , and acts as a leading indicator of their fortunes.

ASML has invested heavily in EUV technology, buying Cymer Inc, a supplier of lithography light sources used to make chips, for $2.5 billion in October 2012 to speed up development of the technology after it suffered a string of setbacks.

Kempen & Co analyst Erwin Dut said the reduction in the sales forecast was a result of ASML having only a few large customers, which can create volatility in quarterly results. But he said the mid- to long-term case for the business was intact.

"It's disappointing but it doesn't really change our case on ASML," said Dut. He has a hold recommendation on the share but is starting to turn more positive.

Around 80 percent of ASML's products go to customers in Asia. The rest are sold to clients in the United States and Europe.

ASML reported first-quarter net profit of 249 million euros, on sales of 1.4 billion euros, roughly in line with forecasts.

It was expected to post first-quarter sales of 1.4 billion euros and a profit of 228 million euros, according to the average of 11 analysts polled by Reuters.

Investors have looked at ASML's investment in EUV technology to gauge future orders and the ability to continue to produce smaller computer chips.

For the second quarter of this year, ASML said it expects sales of 1.6 billion euros, including EUV sales.

($1 = 0.7234 Euros)

(Editing by Miral Fahmy and Mark Potter)