Oliver North, the "action officer" in the Iran-Contra affair, took the stand Thursday at his criminal trial to fight 12 felony charges arising from the worst political scandal of the Reagan administration.

Ramrod straight in his lawyerly blue suit, North placed his left hand on a Bible and said stoutly "I do!" in promising to tell the whole truth about his activities in the foreign policy scandal.His defense lawyer, Brendan Sullivan, leaned over his lectern and said with a smile, "So, you're Colonel North."

"Yes, sir," North replied. "I am."

It never was certain North would take the stand in his 7-week-old trial until he took his place in the witness box. North's wife, Betsy, sat in the front row watching her husband.

The former staff member of the National Security Council was the "action officer" for the U.S. arms sales to Iran and a private airlift that ferried weapons and supplies to the Nicaraguan Contra rebels.

He has claimed all his actions in the foreign policy affair were authorized by his superiors at the White House - including former President Reagan.

Before North's testimony, papers read to the jury showed Thursday that Panama's leader Manuel Noriega offered in 1986 to kill Nicaragua's leaders in exchange for U.S. assistance "to help clean up Noriega's image."

The 44-page "admission" said that in August 1986, North reported to John Poindexter, the national security adviser at the time, that a representative of Noriega told North "that in exchange for a promise from the (United States) to help clean up Noriega's image and a commitment to lift the (U.S.) ban on military sales to the Panamanian defense forces, Noriega would assassinate the Sandinista leadership for the U.S. government."

The paper said North told the representative "that U.S. law forbade such actions" but the strongman's representative replied that Noriega had "numerous assets in place in Nicaragua and could accomplish many essential things."