By Alex Lawler

LONDON (Reuters) - OPEC on Tuesday gave an upbeat outlook for the oil market in 2017, saying global demand for its crude would be higher than its current production and pointing to a supply deficit rather than a sizeable surplus that has weighed on prices.

However, the Organization of the Petroleum Exporting Countries in a monthly report also cut its forecast for world economic growth this year, citing increased uncertainty following Britain's vote to leave the European Union and said the pace of oil demand growth would slow slightly next year, in its first 2017 forecast.

"After the UK's referendum to leave the EU, economic uncertainty has increased," OPEC said in the report. "Potential negative effects have led to a downward revision of global economic growth in 2016 to 3.0 percent from 3.1 percent."

Other forecasters including the International Monetary Fund have cut economic growth outlooks following the UK referendum. Concern about the economic impact of Brexit has weighed on oil prices, which at $47 a barrel have fallen from a 2016 high close to $53 in early June.

World oil demand will rise by 1.15 million barrels per day (bpd) in 2017, OPEC said, its first forecast for next year in the monthly report. That marks a slight slowdown from growth of 1.19 million bpd expected in 2016.

Oil prices have halved from two years ago in a drop that deepened after OPEC refused in late 2014 to cut output to support prices, hoping that cheaper oil would curb higher-cost rival supply such as U.S. shale.

Despite a "dampening effect" of Brexit on the world economy next year, OPEC's 2017 market outlook suggests the strategy is working as it expects oil supply outside the group to fall further, helping to boost demand for its own crude.

OPEC forecasts supply from outside producers will decline by 110,000 bpd in 2017 after an 880,000-bpd drop this year. The price drop since 2014 has hit non-OPEC supply as companies have delayed or canceled projects around the world.

Oil output from OPEC, adjusted to include returning member Gabon, rose 264,000 bpd to 32.86 million bpd in June, OPEC said. It expects demand for its crude in 2017 to average 32.98 million bpd, suggesting a supply deficit if OPEC keeps output steady.

Top exporter Saudi Arabia told OPEC it raised output to 10.55 million bpd in June. The kingdom said it pumped 10.56 million bpd, a record, in June last year.

OPEC's report points to a sizeable average surplus of 1 million bpd this year, but also to demand for its crude exceeding current production in the third quarter. The last full quarter when OPEC pumped less than demand for its crude was in 2013, according to past OPEC reports.

"The contraction seen this year in non-OPEC supply is expected to continue in 2017 but at a slower pace," OPEC said. "Market conditions will help remove overall excess oil stocks in 2017."

Others say it may take until 2018 to erode the excess supply in the market, which they put at 300 million barrels or more.

(Editing by William Hardy and David Evans)