CHICAGO, Jan 27 (Reuters) - Spot basis bids for soybeans and corn were mostly down in the U.S. Midwest on Monday as falling Chicago Board of Trade corn and soy futures discouraged farmer sales, dealers said.

* The soy basis ticked down at a Lafayette, Indiana, processor.

* The corn basis ticked down at an Iowa processor and Illinois processor. The corn basis edged up at a Nebraska elevator.

* Chicago corn and soybean futures fell on Monday as Argentina's cut in grains export taxes raised expectations of larger shipments from the South American producer in competition to U.S. supplies.

* The announcement of Argentine tax cuts put an end to the previous week's rally in corn and soy prices, which had encouraged a flurry of farmer selling.

* Most-active CBOT corn futures Cv1 were last down 7-3/4 cents to $4.78-3/4 a bushel, while most-active soy futures Sv1 were last down 12 cents to $10.43-1/2 a bushel.

Basis values are quoted against CBOT futures in cts/bu:

NOTE: 0 = Option price, UNC = Unchanged, UNQ = Unquoted

NC = Not comparable, DP = Delayed price, N/A = Not available,

F = January, H = March, K = May, N = JulyQ = August, U = September, X = November, Z = December

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LINKS: 0#USCSHGRN-PM

For U.S. forward basis spreadsheets, please click:

CORN/BASIS, SOYA/BASIS, WHEAT/BASIS, MILO/BASIS

- CBOT corn report COR/

- CBOT soybean report SOY/C

- CBOT wheat report WHE/C

- U.S. grain barge freight values BG/US

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

- U.S. CIF/FOB Gulf Grain GRA/F

(Reporting by Heather Schlitz; editing by David Evans)

((Heather.Schlitz@thomsonreuters.com;))