* Russia's 2018 grain crop may total 128.2 mln T - SovEcon
* SovEcon sees 2017/18 ending grain stocks at 31.4 mln T (Adds details, quotes, context)
MOSCOW, Nov 29 (Reuters) - Russia, a major global wheat exporter, is expected to produce another large grain crop in 2018 following a record crop this year and increasing pressure on prices, leading agriculture consultancy SovEcon said on Wednesday.
In the first major estimate for 2018, SovEcon said Russia's grain harvest could amount to 128.2 million tonnes next year after this year's record 134 million tonnes.
Its forecast is preliminary and based on its expectation that the coming winter will be relatively favorable for winter grains, with 6 percent of sowings lost.
"It is a scenario for now, but in any case we face the prospect of a historically high crop of more than 120 million tonnes if (weather) conditions stay at their average level of many years," Andrey Sizov Sr., the head of SovEcon, told a conference in Moscow.
"It means that the market will be in a difficult situation in terms of large grain supplies. One should proceed from the expectation that there will be a lot of grain weighing on the market," he added.
The forecast includes 76.7 million tonnes of wheat in 2018, which would be Russia's second largest wheat crop after a record 83.9 million tonnes this year.
Harvesting in Russia, expected to become the world's largest wheat exporter in the 2017/18 marketing year which runs until June 30, is almost complete. But officials have yet to announce the size of the 2017 crop after drying and cleaning.
This year's crop will leave Russia with a record 46 million tonnes of grain available for export in 2017/18, according to SovEcon.
"We expect significant growth in grain and wheat stocks despite these huge exports," said SovEcon managing director Andrey Sizov Jr.
The consultancy expects a 55-percent year-on-year rise in ending stocks to a record 31.4 million tonnes by June 30, 2018.
For wheat, that will mean a crop of 83.9 million tonnes with 35 million tonnes of exports in 2017/18 and 21.8 million tonnes of stocks by June 30, 2018, it added.
Russia exported 20.2 million tonnes of grain, including 15.6 million tonnes of wheat, between July 1 and Nov. 22, up 27.6 percent from the same period a year ago. Grain stocks were up 16 percent year-on-year at 56 million tonnes as of Nov. 1. (Reporting by Polina Devitt; Editing by Greg Mahlich and Mark Potter)