(Adds bonds, peso, details)
BUENOS AIRES, Sept 19 (Reuters) - Argentine stocks closed 10.24 percent higher on Friday, marking their biggest one-day jump since January 2002 as global markets rallied on optimism over a U.S. financial rescue plan.
The MerVal .MERV benchmark stocks index ended at 1,662.52 points, largely neutralizing steep losses seen the rest of the week.
"Obviously the plan to rescue the U.S. financial system has brought some calm to investors," said Francisco Marra, a trader at Bull Markets Brokers. "The MerVal is accompanying the worldwide gains."
The U.S. government unveiled a plan to pledge $50 billion to guarantee safe-haven, money-market mutual funds, and officials are working on a solution to take over hundreds of billions of dollars worth of bad mortgage debts.
Trade volume on Argentina's broad stock market was a brisk $50.6 million. Among active shares, 98 advanced, 10 retreated and six were unchanged.
Meanwhile, locally traded sovereign debt rose by 4.5 percent on average in over-the-counter trade <AR/BONOS>, with peso-denominated Discount bonds leading gains.
The peso currency firmed against the dollar after weakening earlier in the week as the global economic doom saw savers and investors rush into greenbacks.
The peso closed just 0.08 percent stronger at 3.1150/3.1175 per dollar ARS=RASL in formal interbank trade, where the central bank regularly intervenes.
In informal trade between foreign exchange houses, as measured by Reuters, it firmed 1.27 percent to end at 3.1550/3.1600 per dollar ARSB=. (Reporting by Jorge Otaola and Walter Bianchi; Writing by Hilary Burke; editing by Gary Crosse)