UPDATE 1-Citrix Systems expects profit below Street

* Expects Q3 adj EPS $0.64-$0.66 vs est $0.71

* Sees Q3 rev $645-$655 mln vs est $646.1 mln

* Q2 adj EPS $0.71 vs est $0.59

* Q2 rev up 16 pct at $615 mln vs est $613.2 mln

* Shares down 3 pct after market

July 25 (Reuters) - Citrix Systems Inc's quarterly results beat Wall Street estimates, but the business software maker forecast weak third-quarter earnings on an uncertain global economy, sending its shares down 3 percent in extended trading.

Citrix forecast third-quarter earnings of 64 cents to 66 cents per share, on revenue of $645 million to $655 million.

Analysts were looking for earnings of 71 cents per share, on revenue of $646.1 million, according to Thomson Reuters I/B/E/S.

The company also announced it would buy back up to an additional $400 million of its common stock.

Net income for the second quarter rose to $92 million, or 49 cents a share, from $82 million, 43 cents, a year earlier.

Excluding items, Citrix, which competes with VMware Inc , earned 71 cents per share.

Its revenue increased 16 percent to $615 million.

Analysts had expected earnings of 59 cents per share, on revenue of $613.2 million.

Shares of the Fort Lauderdale, Florida-based company closed at $75.11 on Wednesday on the Nasdaq. They were down at $72.14 after the bell.