Nov 26 (Reuters) -Spot basis bids for soybeans shipped by barge to the U.S. Gulf Coast slipped on Tuesday, traders said, after higher water levels in Midwest rivers improved shipping conditions.

* Heavy rainfall across the central United States has brought relief to Gulf Coast grain shippers, bolstering crop supplies at the Gulf.

* Still, Brazilian soybeans are offered cheaper than U.S. soybeans at the Gulf.

* Traders are waiting to see how U.S. President-elect Donald Trump affects grain trading with plans to impose big tariffs on the three largest U.S. trading partners - Canada, Mexico and China.

* Trump has outlined "an additional 10% tariff, above any additional tariffs" on imports from China, the biggest soybean importer. He also pledged to impose a 25% tariff on imports from Canada and Mexico, the biggest U.S. corn buyer.

* Soybean futures were lower at the Chicago Board of Trade amid expectations for U.S. exports to slow after Trump's inauguration on Jan. 20, said Terry​​​​ Reilly, senior agricultural strategist for Marex. CBOT corn was under pressure from concerns Mexico's buying will dry up if they retaliate against U.S. import tariffs, he said. GRA/

* CIF Gulf soybean barges loaded in November were bid 86 cents over Chicago Board of Trade January soybean SF25 futures, down a penny from Monday. December soy barge bids were bid 84 cents over futures, also down a penny.

* Tight spot loading capacity at Gulf terminals has underpinned spot values.

* FOB export premiums for soybeans shipped from the Gulf in December were steady at about 115 cents over January futures. January offers stayed at 108 cents over futures.

* CIF corn barges loaded in November were bid flat at 80 cents over CBOT December CZ24 futures, while December barges were bid steady at 81 cents over futures.

* FOB offers for January corn shipped out of the Gulf, the first month available, were flat at 92 cents over CBOT March CH25 futures.

Reporting by Tom Polansek; Editing by Shounak Dasgupta

For displays of CIF basis, click on the codes in brackets: U.S. CIF Gulf soybeans GRYM U.S. CIF Gulf corn GRYN U.S. CIF Gulf SRW wheat GRYO U.S. CIF Gulf HRW wheat GRYP
For displays of FOB basis, please click on the following codes in brackets: U.S. FOB Gulf corn GRZC U.S. FOB Gulf soybeans GRZD U.S. FOB Gulf SRW wheat GRZE U.S. FOB Gulf HRW wheat GRZF LINKS Corn prices page: cpurl://apps.cp./cms/?pageid=corn-cash-market
Wheat prices page: cpurl://apps.cp./cms/?pageid=wheat-cash-market
U.S. barge freight BG/US
U.S. export sales estimates USDA/EST
U.S. grain export summary GRA/U
Brazil soybean export prices SYBS
Brazil corn export prices SYBX
Argentina grain prices GRA/ARG
Russia grain prices GRA/RU