Oliver North let co-defendant Richard Secord pay for a security fence at his home and then tried to cover up the transaction after he left the White House, a security consultant testified Tuesday.

Glenn Robinette, who worked for the CIA for 21 years, told the North jury that he had the $13,800 security system installed at North's home in Great Falls, Va., in mid-1986 and collected $16,000 for the work from Secord.After North was fired from the White House in November 1986, he telephoned Robinette and said, "Hey buddy, you never sent me a bill for that security work you did for me," Robinette testified at North's trial in U.S. District Court on charges of obstructing Congress and other alleged offenses.

Robinette said that when he had estimated the cost at $8,000 at a May 10, 1986, meeting, North told him, "I am on a poor lieutenant colonel's pay so do your best to keep it around that figure."

The security consultant said he then sent North two phony bills backdated to July 2, 1986, and Sept. 22, 1986, and North sent Robinette letters backdated to May 18, 1986, and Oct. 1, 1986, outlining a plan to pay for the work by offering his commercial endorsement of the system once he retired from the Marines.

North is accused of accepting an illegal gratuity from Secord, who was enlisted by the fired White House aide to secretly run arms to the Contras.

Prosecutor John Keker disclosed out of the presence of the jury that Robinette lied to a federal grand jury in 1987 by denying that Secord paid for the fence and saying that the backdated exchange of correspondence was real. Keker said Robinette later recanted.

Robinette testifed about the fence to Congress in 1987.

In court, Robinette described how, prior to his grand jury testimony, North telephoned him and requested a meeting to which Robinette was to bring the phony correspondence. The meeting occurred in March 1987.

After allowing North's lawyer to get copies of the correspondence, Robinette said he immediately went to a meeting with Secord, who now is charged with conspiring with another co-defendant, Albert Hakim, to offer illegal gratuities to North, including the security fence.

North said he needed the security system because someone had been putting sand in his gas tank, flattening his tires, flashing lights outside his home and leaving packages in the mailbox.