UPDATE 2-Seagate estimates revenue below forecast

* Sees Q4 rev of $4.5 bln

* Says supplier's quality issue hit production

* Shares down 6 pct afterhours (Adds details)

July 5 (Reuters) - Electronic storage device maker Seagate Technology Plc said its fourth-quarter revenue is expected to have missed its forecast as a quality issue at a supplier affected production in its enterprise disk drive unit.

The company, which competes with Western Digital Corp and Sandisk Corp, said shipments fell by about 1.5 million units to about 66 million for the June quarter, squeezing adjusted gross margins to 33.6 percent.

The company now expects to report revenue of $4.5 billion. It had forecast $5 billion.

Analysts on average were expecting revenue of $4.88 billion, according to Thomson Reuters I/B/E/S.

The company also said it was adjusting its production according to lower global demand.

"We are adjusting our production and inventory planning accordingly, and we expect average selling prices and margins to remain relatively stable in the September quarter," Chief Executive Steve Luczo said in a statement.

Shares of the company were down 6 percent at $23.62 in trading after the bell. They closed at $25.08 on Thursday on the Nasdaq.

Western Digital's shares were down 4 percent at $29.60 after the bell. (Reporting by Chandni Doulatramani in Bangalore; Editing by Don Sebastian)