Police today said National Guardsmen foiled El Salvador's latest kidnap bid, as the son of a banker kidnapped over the weekend pleaded with the abductors to release his father and take him captive instead.

Police said one National Guardsman was killed and another wounded Monday, when masked men attempted to seize wealthy coffee grower Pedro Mendez Castro in the city of Santa Ana 40 miles east of San Salvador.

In radio and newspaper advertisements Monday, Luis Escalante Sol offered himself in exchange to the unidentified leftists who last Saturday kidnapped his banker father, Luis escalante Arce.

The elder Escalante, 65, is thought to have been wounded resisting the kidnapers.

Meanwhile, a terrotist group has demanded that an American company buy newspaper space for revolutionary messages in U.S. and Central American newspapers before it releases two American employes kidnaped in San Salvador last month, the company said.

A spokeman for the Californiabased Beckman Instruments, Inc., said the first two ads will appear in Wednesday's editions of the Los Angles Times and The New York Times. He said the message urges support of the Revolutionary Party of Central American Workers, which has claimed responsibility for the Sept. 21 kidnaping of Dennis McDonald and Fausto Bucheli and the slaying of their Salvadoran bodyguard.