* FTSE 100 up 0.3 percent
* Budget due at 1230 GMT
* Supermarkets weaker after Sainsbury results
* Banks weighed by worries on euro zone debt
By Simon Falush
LONDON, March 23 (Reuters) - Miners buoyed by rising metal prices pushed Britain's top shares higher by midday on Wednesday, as investors' optimism about the corporate earnings outlook trumped global political and economic worries.
However Sainsbury tumbled, bringing peers lower after it missed sales forecasts, underlining the tough economic backdrop against which Britain's finance minster will reveal the national budget at 1230 GMT.
By 1135 GMT, the FTSE 100 was up 147.69 points, or 0.3 percent, at 5,780.40, having closed down 0.4 percent on Tuesday.
The index has gained for three of the last four sessions but is still down over 3 percent in March as political turmoil and violence across the Arab world and the massive earthquake and nuclear crisis in Japan saw investors sell riskier assets.
"Risks came to the fore and then faded back as the market needs to move on," said Philip Poole, global head of macro investment strategy at HSBC Global Asset Management.
"Interest rates will stay low, there will be more quantitative easing and there's a lot of cash out there that investors will want to make work for them when the risks are clearer."
Kazakh miner ENRC topped the list of blue-chip gainers, up 3.9 percent, after it met forecasts with full-year underlying profit that more than doubled.
This cheered other miners that were also lifted as copper prices rose, with mining executives saying that reconstruction in Japan after the earthquake and tsunami would be bullish for metals.
Analysts saw potential for more gains in equities.
"We are still positive on equities in our asset allocation as prospective P/E ratios and book values are below average," said Keith Wade, chief economist and strategist at Schroders, which has 197 billion pounds ($322.5 billion) under management.
SAINSBURY SLIDES
Sainsbury slipped 5.3 percent as its fourth-quarter sales failed to meet expectations, adding to signs of a slowdown in consumer spending growth as inflation climbs and government cuts bite.
Gloom on the outlook for grocery spending pushed peers Tesco and Morrison 1.9 and 1.2 percent lower respectively.
Marks & Spencer, however, added 2.4 percent, as prospects for its clothing business were helped by Spain's Inditex, the world's largest clothing retailer, posting a 32 percent jump in annual net profit.
Banks were a drag on the index ahead of a crucial vote in the Portuguese parliament that could bring down the government, a reminder that the euro zone's debt crisis is far from resolved.
The UK budget statement is expected to see Britain's coalition government seeking to bolster a faltering economy without compromising its austerity programme.
For a preview of the UK Budget, double click on
The Bank of England's Monetary Policy Committee remained divided on whether to raise interest rates this month and appeared no closer to tightening policy than they were in February.
This slightly boosted the FTSE as some investors thought there was a chance that more members may have voted for a rise, which would hit growth prospects.
Ex-dividend factors knocked 2.2 points off the FTSE 100 index on Wednesday, with Aviva, InterContinental Hotels, and Schroders all trading without their dividend attractions. (Editing by Erica Billingham)