* CBOT soy drops 3.2% this week

* Weekly U.S. grain export sales miss estimates

* USDA crop data due out next week

CHICAGO, Jan 5 (Reuters) - Chicago Board of Trade soybean futures crumbled to their lowest prices since June on Friday and declined for a third consecutive week as much-needed rains hit dry growing areas in Brazil.

Corn futures set a contract low. Wheat prices advanced but still finished the first week of 2024 in negative territory.

The setback in soybean futures came as rains have reduced concerns about crop losses in the world's biggest exporter of the oilseed. Stabilizing yields could prevent soy buyers from shifting export business to the U.S. from Brazil, as the nations compete for sales on the world market.

For the week, soybean futures lost about 3.2%, while corn fell 2.2% and wheat slid 1.9% at the CBOT.

"It's been lower this week as we came back from the holiday," said Sherman Newlin, an Illinois farmer and analyst with Risk Management Commodities. "It's been based off of all the rain that's been going on in South America."

Most-active CBOT March soybeans ended down 11-1/4 cents at $12.56-1/4 a bushel after reaching the lowest price since June 15.

March corn futures finished 5-3/4 cents lower at $4.60-3/4 per bushel and reached a contract low at $4.60. March wheat settled up 2-1/2 cents at $6.16 per bushel as the market bounced from a one-month low on Thursday.

Weak U.S. export demand hung over the markets, as Brazilian exporters group Anec projected Brazil's soy shipments will rise this month from a year earlier.

The U.S. Department of Agriculture reported on Friday export sales of U.S. 2023/24 soybeans in the week ended Dec. 28 were 201,600 metric tons, below analysts' expectations for 500,000 to 1,300,000 tons. Weekly U.S. corn and wheat sales also missed expectations.

Next week, the USDA is slated to issue a quarterly U.S. grain stocks report and monthly data on global supply/demand. Agribusiness consultancy Safras & Mercado lowered its forecast for Brazil's crop to 151.36 million metric tons from 158.23 million. (Reporting by Tom Polansek in Chicago. Additional reporting by Naveen Thukral in Singapore and Sybille de La Hamaide in Paris; Editing by Sonia Cheema, Mark Potter, David Gregorio and Jonathan Oatis)