* Investor jitters ease after Iran missile strike in Iraq
* Mideast tensions, swine fever in China cloud demand outlook
* Grain market awaits USDA crop data, U.S.-China deal terms (Adds closing prices, updates lead, changes headline)
CHICAGO, Jan 8 (Reuters) - Chicago soybean and grain futures were narrowly mixed on Wednesday as traders' jitters eased after Iran and the United States signalled a de-escalation of tensions after an Iranian missile attack against U.S. forces in Iraq.
Investors also continued to square positions ahead of a key U.S. Department of Agriculture (USDA) crop supply-and-demand report due at the end of the week.
The most-active soybean contract on the Chicago Board Of Trade settled up 3-1/4 cents at $9.47-1/4 a bushel, after dipping slightly earlier in the day.
CBOT corn closed the day down 1/4-cent to $3.84-1/4 a bushel, while wheat rose 2-1/2 cents to $5.52-3/4 a bushel.
Iran said it launched a missile attack on U.S.-led forces in Iraq in the early hours of Wednesday in retaliation for a U.S. drone strike last week that killed Iranian commander Qassem Soleimani.
But U.S. President Donald Trump said on Wednesday there were no American casualties in the Iranian strikes on military bases housing U.S. troops in Iraq and that Tehran appeared to be standing down.
For now, traders said, crop markets are focused on the USDA report, set for Friday, which could include a revision to the U.S. corn harvest after adverse weather conditions.
"The greatest unknown in these numbers is what is done with the unharvested crops," such as North Dakota, where many corn fields remain standing due to weather issues, said Karl Setzer, commodity risk analyst for AgriVisor.
Grain traders said they are also waiting for more details on the Phase 1 U.S.-China trade deal due to be signed next week, which calls for bigger Chinese purchases of U.S. agricultural goods.
Brazil could lose some gains it made in the global soy market during the U.S.-China trade war in the event that the two countries close a deal ending the dispute, a Brazilian Agriculture Ministry official said on Wednesday.
However, a Chinese media report on Tuesday that said Beijing would not expand wheat, corn and rice import quotas to accommodate extra U.S. farm products encouraged caution over the trade deal.
Beneficial rainfall for corn and soybean crops in Brazil and Argentina were also keeping a lid on Chicago futures.
The wheat market was awaiting the outcome of a tender by top importer Egypt. No U.S. wheat was offered but initial bids showed a sharp increase in prices compared with a previous Egyptian tender a month ago. (Reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore, Editing by Paul Simao and Cynthia Osterman)