CHICAGO, May 21 (Reuters) - Spot basis bids for hard red winter (HRW) wheat were mostly unchanged at elevators and mills around the southern U.S. Plains on Wednesday, capped by firm futures prices, grain merchants said.

• Rising futures prices have sparked some light, scattered farmer sales this week, merchants said. But the overall pace of sales has been minimal as many growers are seeking even higher prices, merchants said.

• Export demand has been rising as U.S. wheat is competitively priced in the global market, traders said.

• Analysts surveyed by Reuters ahead of Thursday's weekly U.S. Department of Agriculture export sales report expect net old-crop sales in the week ended May 15 at up to 100,000 metric tons while new-crop sales were seen as high as 700,000 tons.

• CBOT July K.C. HRW wheat KWN25 futures were 2-1/2 cents higher near the close on Wednesday at $5.38-3/4 a bushel, having earlier touched a 3-1/2 week high.

Basis values are quoted against futures in cts/bu:

NOTES:

H = March, K = May, N = July, U = September

Z = December; UNQ = Unquoted bids

0 = Sp Option price; NC = No comparison

* = No. 1 12% hard winter wheat, rail bids

** = Ordinary protein, rail bids

LINKS:

* K.C. HRW wheat protein scales KCBT/SCA

* U.S. weekly wheat crop progress US/WHE

* U.S. forward basis WHEAT/BASIS

* U.S. Midwest cash grain PM GRA/PM

* U.S. CIF Gulf Grain GRA/C

* U.S. FOB Gulf Grain GRA/F

(Reporting by Karl Plume in Chicago, Editing by Nick Zieminski)

((karl.plume@thomsonreuters.com; +1 313 484 5285))