* CBOT soybeans rise as U.S. crop ratings drop

* USDA to issue grain stocks report on Fri

* Traders eye potential U.S. government shutdown

Sept 26 (Reuters) -

Chicago soybean futures ticked higher on Tuesday while wheat futures settled flat and corn futures fell as traders adjusted positions ahead of U.S. government stocks data due later this week, analysts said.

Worries about a possible U.S. government shutdown hung over the markets.

Chicago Board of Trade (CBOT) November soybean futures rose 5 cents to settle at $13.02-3/4 a bushel, closing above $13 for the first time since it fell below what some traders saw as a key technical level last week.

December wheat touched a one-week high of $5.96-3/4 a bushel before falling back to settle unchanged at $5.89. December corn ended down 1-1/2 cents at $4.79-3/4 a bushel after hitting $4.83-1/2, its highest price in over a week.

The U.S. Department of Agriculture (USDA) is slated to issue a closely watched, quarterly report on U.S. grain stocks at the end of the week.

"A lot of what we're seeing today is positioning ahead of Friday," said Karl Setzer, brokerage research lead for Bloomington, Illinois-based MidCo Commodities.

Setzer said the prospect of a U.S. government shutdown was another factor keeping prices in check.

"It's everything moving toward a point where there's just not a lot of interest," he said.

Wheat prices saw an early bounce after recent Russian attacks on Ukrainian ports, while an unofficial minimum price for Russian wheat exports was also raising questions about Black Sea supply. Some of these concerns, though, have been offset by Russia's massive wheat harvest.

For soybeans, large supplies from Brazil have hampered demand for U.S. exports, while tight U.S. supplies have kept domestic prices elevated above the global market, analysts said.

A weekly USDA report released late on Monday showed 50% of the U.S. soybean crop rated "good" or "excellent," down from 52% in the previous week and the lowest for this time of year since 2013. The ratings add to concerns over production prospects after the USDA on Sept. 12 forecast U.S. soybean output would fall to a four-year low. (Reporting by Zachary Goelman in New York City; additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by David Gregorio)