* Dryness seen trimming soybean yields

* Market awaits USDA crop ratings, Pro Farmer tour results

* Wheat eases after Friday rally

PARIS/SINGAPORE, Aug 21 (Reuters) - Chicago soybeans rose for a fourth straight session on Monday to reach their highest in more than three weeks as hot, dry weather in the U.S. Midwest fuelled concern over crop stress.

Corn prices edged higher, underpinned by weather worries as grain markets awaited results from the annual Pro Farmer crop tour, which will examine corn and soybean fields across the Midwest this week.

Wheat ticked lower, pausing after Friday's rally as participants assessed Ukrainian efforts to maintain grain exports despite recent military escalation and Russia's withdrawal from a wartime shipping agreement.

The most active soybean contract on the Chicago Board of Trade (CBOT) was up 1.6% at $13.74-1/2 a bushel by 0842 GMT, having earlier touched its highest since July 28.

Corn added 0.7% to $4.96-1/2 a bushel as it moved further away from last week's 2-1/2 year low.

"The 40 degrees Celsius (104 Fahrenheit) mark is expected to be reached in the western corn belt as the traditional and closely watched Pro Farmer Crop Tour gets under way this Monday," consultancy Agritel said in a note.

"In corn, the critical pollination phase has passed, but it is soybeans in particular that are currently in their most sensitive flowering stage."

The market is also awaiting weekly U.S. Department of Agriculture crop ratings due after the market close on Monday to see if dry weather last week has already strained some crops.

The shift in U.S. weather in the past week has supported prices that had been pressured by recent rainfall in the Midwest and wider investor worries over China's economy.

CBOT wheat was down 0.5% at $6.36 a bushel, retreating after initially extending Friday's sharp gains to reach its highest since Aug. 9.

Latest military incidents in the Russia-Ukraine war sparked short-covering on Friday as the threat of further disruption to Black Sea grain trade hung over the market.

However, Ukrainian moves to maintain its exports, as well as ongoing Russian shipments, were tempering supply fears.

Ukraine is considering using its newly tested Black Sea export corridor for grain shipments in future after evacuating a blocked container ship via this route, a senior agricultural official said.

Ukraine is also finalising a scheme with global insurers to cover grain ships travelling to and from its Black Sea ports, the Financial Times reported, citing Deputy Economy Minister Oleksandr Gryban. (Reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore Editing by Sherry Jacob-Phillips and David Goodman)