* Sees Q2 revenue about $161 million

* Forecast for Q2 rev was $168-$173 mln

* Says resetting FY09 rev view to $690-$720 mln

* Shares down 21 percent (Recasts, adds details)

July 1 (Reuters) - Illumina Inc (ILMN.O: Quote, Profile, Research) reported a lower-than-expected second-quarter revenue as customers delayed purchase of its arrays, and cut its 2009 revenue view, sending its shares tumbling 21 percent after the bell.

The company cited the impact of reduced foundation funding in a few key accounts and order delays tied to stimulus funding under the American Recovery & Reinvestment Act, for the lower revenue.

Illumina expects the academic and research stimulus funding to have a positive impact in fourth quarter and in 2010, but not in the short term.

"The program has caused order delays as customers wait to learn whether and to what extent they will receive incremental funding," the company said in a statement.

Illumina, which makes tools for genetic analysis, said the delay in purchase decision by its customers has reduced revenue by about $10 million to $15 million in the first half of 2009.