GLOBAL MARKETS-Asia shares rise, sterling steady as Brexit vote looms

* Wall Street gains as polls tip "Bremain" gaining ground

* Yellen's testimony awaited ahead of Thursday's UK vote

* Crude oil futures give back some of overnight surge

By Lisa Twaronite

TOKYO, June 21 (Reuters) - Asian shares rose after a tentative start on Tuesday, cautiously extending a rally triggered by growing expectations that British voters will opt to remain in the European Union in this week's referendum.

MSCI (NYSE: MSCI - news) 's broadest index of Asia-Pacific shares outside Japan was up 0.2 percent.

Investors remain wary ahead of Thursday's British vote, as well as Federal Reserve chief Janet Yellen's two-day testimony before Congress starting later on Tuesday, as she might offer clues on the timing of the next U.S (Other OTC: UBGXF - news) . interest rate increase.

"With Yellen's congressional testimony and the UK referendum on our doorstep, markets all around are exercising caution," said Andrew Meredith, co-managing director at Tyton Capital Advisors.

Bookmakers' odds have also shown "Remain" gaining traction in Britain's referendum, with Betfair putting the implied probability of such an outcome at 72 percent on Monday, up from 60-67 percent on Friday.

Two of the latest polls released over the weekend showed the "Remain" camp in the lead, reversing a recent rise in support for pulling out and prompting a rally in global equities and the pound on Monday.

"The polls were not supposed to influence as much as they have, but overnight we have seen a rampant position adjustment and an unwind of 'Brexit' hedges," wrote Chris Weston, chief market strategist at IG (LSE: IGG.L - news) in Melbourne.

(For the latest Reuters news on the referendum including full multimedia coverage, click )

Japan's Nikkei stock index reversed early losses and added 0.5 percent.

A Reuters poll showed that confidence at Japanese manufacturers inched up in June from the prior month's three-year low and is seen rising only slightly ahead, reflecting worries about the yen's rise ahead of the British vote.

Minutes of the Bank of Japan's April meeting released on Tuesday showed policymakers believe overseas economies continue to pose downside risks to Japan's economy and prices.

The pound was steady on the day at $1.4670 after it rose as high as $1.4721 on Monday, extending a recovery from last Thursday's more than two-month trough of $1.4013.

The dollar added 0.1 percent to 103.98 yen, moving away from Thursday's nearly two-year low of 103.55 that was hit after the BOJ held policy steady, disappointing investors hoping for more stimulus.

The euro gained 0.2 percent to $1.1336.

Later in the session, Germany's constitutional court will rule on the emergency bond-buying plan devised by the European Central Bank during the financial crisis. An outright rejection of the programme is viewed as unlikely, but the ruling could potentially upset the ECB's current programme and roil markets.

Crude oil futures gave back some of their gains after surging 3 percent on Monday as "Brexit" fears waned.

Brent crude shed 0.5 percent to $50.41 a barrel, while U.S. crude was down 0.4 percent, at $49.19.

(Editing by Simon Cameron-Moore)