U.S. stocks edged up on Wednesday and the euro held steady against the dollar on lingering hopes an EU summit can ease Europe's debt crisis.

But U.S. Treasuries rose as some investors remained pessimistic about the summit, buying into safe-haven bonds.

Commodities saw a clearer risk-off trade, with oil, metals and grains prices falling broadly.

Stocks were besieged by volatility from start to finish, with razor-thin volumes exaggerating market moves. Wall Street's S&P 500 index fell by up to 1 percent at one point, before recovering more than half of the dip within minutes.

The choppy session followed gains in U.S. stocks since the start of the week, built on the notion that the European Union summit beginning Friday will create a more workable solution to the bloc's debt crisis.

I think the hopes (for a deal in the summit) are certainly still there. There's a belief in the marketplace that the euro zone doesn't have a death wish, said Art Hogan, managing director at Lazard Capital Markets in New York.

The Dow Jones industrial average <.DJI> closed up 46.24 points, or 0.38 percent, at 12,196.37. The Standard & Poor's 500 Index <.SPX> was up 2.54 points, or 0.20 percent, at 1,261.01. The Nasdaq Composite Index <.IXIC> was down 0.35 points, or 0.01 percent, at 2,649.21.

Since reaching a closing low on November 25, the S&P 500 had risen almost 9 percent through Wednesday on hopes for a credible outcome to the summit.

We'll probably keep seeing volatility until we see the plan, and if it disappoints we could drop 2 or 3 percent, said James Dailey, portfolio manager of TEAM Asset Strategy Fund in Harrisburg, Pennsylvania.

Expectations on the summit have been high, with investors hoping it will help stave off a broader downgrade of European nations by Standard & Poors.

French officials had said earlier this week that French and German leaders will not leave the summit until a powerful deal was reached.

But a German government official discounted such hopes on Wednesday, saying Berlin was getting increasingly pessimistic about the summit.

Standard & Poors cautioned on Monday that it had 15 of the euro zone's 17 members on a credit watch for a potential downgrade. On Wednesday, the rating agency said it may lower the EU's AAA long-term issuer rating, if it cuts the current AAA ratings in one or more member states.

Any reticence on the part of Germany is going to be viewed as a setback, said Jack Ablin, chief investment officer at Harris Private Bank in Chicago.

Lazard's Hogan concurred with that. In another time, the market would be down much more than it is.

The euro held its ground against the dollar <.DXY>, even after Standard & Poor's also placed the European Union on credit watch.

The benchmark 10-year U.S. Treasury note was up 16/32, with the yield at 2.0296 percent.

The FTSEurofirst 300 index for European stocks <.FTEU3> finished down 0.1 percent loss, after rising 0.6 percent earlier in the session.

Global equities, however, rebounded, with the MSCI world stocks index <.MIWD00000PUS> up 0.4 percent after moving between negative and positive territory.

Crude oil prices in London fell more than a dollar to below $110 a barrel, pressured by the euro crisis and a surprise jump in U.S. crude stockpiles.

Benchmark copper on the London Metal Exchange closed down $15 at $7,820 a tonne.

The benchmark 10-year U.S. Treasury note was up 15/32 in price, its yield at 2.0331 percent.

(Additional reporting by Rodrigo Campos and Ryan Vlastelica in New York and Richard Hubbard in London; Editing by Theodore d'Afflisio and Andrew Hay)