* Third monthly decline from a year earlier
* Molybdenum output rises 31 pct year-on-year (Adds molybdenum output, background)
SANTIAGO, May 30 (Reuters) - Chile's copper output CLCOPP=ECI fell 3.9 percent in April compared with a year earlier to 438,340 tonnes, the National Statistics Institute (INE) said on Monday.
April was the third straight month that copper production fell from a year earlier in Chile, the world's top producer.
Chile, which holds by far the world's top copper reserves, is expected to steadily increase output in the next two years with new mine projects and upgrades.
The country's molybdenum output rose 31 percent in April from a year earlier to 3,597 tonnes. (Reporting by Moises Avila; Editing by James Dalgleish)