UPDATE 1-Sonic Corp Q4 comp sales fall 6.4 pct

* Comp-sales at company-owned drive-ins fall 6.1 pct

* Sees slight improvement in restaurant margins for FY 2011

* Shares fall 5 pct in extended trade

Sept 14 (Reuters) - Drive-in restaurant chain Sonic Corp (SONC.O) reported a 6.4 percent decline in fourth-quarter same-store sales, sending its shares down 5 percent after the bell.

Sonic, whose sales have been hit due to the high unemployment rates among its core demographics, said same-store sales in its drive-ins were down 6.1 percent for the quarter.

For fiscal 2011, the company expects slight improvement in restaurant-level margins as a result of labor efficiencies, it said in a statement.

Sonic expects improvement in same-store sales in 2011, as its sales initiatives boost traffic, the company said.

Weaker spending by youth, who account for a large number of fast-food customers, has hurt sales at fast food chains including Sonic.

Shares of the company, which have lost about 18 percent of its value since it reported its third-quarter results, closed at $7.65 Tuesday on Nasdaq.

(Reporting by NR Sethuraman in Bangalore; Editing by Prem Udayabhanu)