* European bourses, euro struggle on Spain, Greece, Brexit rumblings

* Dollar pulls off 6-month low after Trump worries last week

* Oil hits $54 per barrel on OPEC hopes

By Marc Jones

LONDON, May 22 (Reuters) - European shares, the euro and the pound all stumbled on Monday as rumblings in Spain, Britain and Brussels reminded investors that the region still has plenty of political uncertainty left in the tank.

A one-month high for oil and bounce in the dollar had triggered Asia's best session in weeks overnight but Europe struggled to maintain the momentum early on.

The euro and Spanish stocks and bonds all saw a soft start as one of the most outspoken critics of Mariano Rajoy's ruling party and Spain's austerity policies returned to front the opposition Socialists.

Britain's pound was also in the firing line, back below $1.30, as polls showed the country's election race tightening and its chief Brexit negotiator again threatened to walk away from EU exit talks unless the bloc eased its demands.

"Last week was all about U.S. uncertainty but we have had a reminder that Europe still has plenty of uncertainty too," said Alvin Tan at Societe Generale.

The dollar, meanwhile, pulled off a six-month low after concerns about Donald Trump's firing of a former FBI head and his administration's links to Russia had given the greenback a drubbing last week.

The dollar index, which tracks the U.S. currency against a basket of six major rivals, rose 0.2 percent while futures markets pointed to a steady start for Wall Street when trading resumes.

Net long positioning on the euro versus the dollar rose to its highest in more than three years last week Commodity Futures Trading Commission data showed on Friday.

But Citi's 'economic surprise' indicators show the recent bout of negative U.S. economic surprises may now be bottoming out. Analysts are also waiting for this week's release of the Federal Reserve meeting minutes.

"Our bias is still dollar positive," said Adam Cole, currency strategist at RBC Capital Markets in London.

Oil also rose on Monday, bolstered by confidence that top exporters will at least agree to extend supply curbs at an OPEC meeting this week, with suggestions that the cuts could even be deepened.

Brent crude was up 40 cents at $54.00 a barrel, with U.S. light crude 38 cents at $50.71. Both benchmarks have climbed more than 10 percent from lows hit earlier this month.

"The decision (to extend cuts) seems to be almost a done deal," said Bjarne Schieldrop, chief commodities analyst at SEB Markets. "There seems to be a very high harmony in the group."

GREECE

Another familiar European story was also back on the radar.

Euro zone finance ministers and the IMF will meet later on Monday to try and nail down a deal on Greek debt relief that balances the IMF's demand for a clear "when and how" with Germany's preference for "only if necessary" and "details later".

Without the loans, Athens would be likely to default whereas country wants a deal to help it return to market financing next year when its latest bailout, the third since 2010, ends in mid-2018.

In Asia, MSCI's broadest index of Asia-Pacific shares outside Japan enjoyed its best session in a month helped by gains in Australia and Hong Kong stocks despite a mass downgrade of bank credit ratings in the former and new property market regulations in the latter.

Chinese stocks were the only laggards in the region with mainland indices ending 0.5 percent in the red as concerns also simmered about another dip in the economy there.

The bounce in Asian stocks this year has helped MSCI's closely followed emerging stocks index notch up gains of more than 17 percent compared to 8 percent for the wider 'all-world' index which is near a record high.

For Reuters Live Markets blog on European and UK stock markets see reuters://realtime/verb=Open/url=http://emea1.apps.cp.extranet.thomsonreuters.biz/cms/?pageId=livemarkets (Additional reporting by Ritvik Carvalho in London; Editing by Toby Chopra)