Betsy North, wife of former White House aide Oliver L. North, invoked the Fifth Amendment against self-incrimination when called recently before a federal grand jury investigating the Iran-contra affair, according to informed sources.

She has also refused to cooperate with the House and Senate select committees investigating the scandal, although the committees have decided not to pursue legal avenues that would compel her testimony, the sources reported.

Investigators are particularly interested in Betsy North's testimony regarding approaches by a representative of Albert A. Hakim, a financier who worked with Oliver North in the private network that carried out the Iran and contra intiatives for the White House, and who sought to channel money to the North family.

Hakim had already established a $200,000 Swiss bank account that he said was to be a "death benefit" for North. Last October, he arranged for his Switzerland-based lawyer, Willard I. Zucker, to contact Betsy North and meet with her to determine what Hakim called a "proper way" to channel money to the North family.

It is not clear what, if any, further steps independent counsel Lawrence E. Walsh might take to compel testimony from her.

Meanwhile, the chairmen and vice chairmen of the House and Senate select committees met yesterday afternoon to map strategy for the next six weeks of investigation and hearings.

Today and Thursday, lawyers for the committees will question in secret the two principal witnesses. Former national security adviser John M. Poindexter is scheduled to be interrogated for the second time today, and North will answer questions in a private deposition for the first time on Thursday, informed sources said.

The committee leaders agreed yesterday to stick to a schedule that would end the hearings around Aug. 7.

Some Democrats on the House and Senate committees said privately in the past few days that they believe the investigation is being rushed to meet an arbitrary deadline. Both groups of Democrats reportedly favor more extensive public hearings on aspects of the scandal that a tight deadline would preclude.

Some House Democrats, anxious to pursue possible fund-raising abuses by the White House, want to call Carl R. (Spitz) Channell, who has pleaded guilty to conspiring to defraud the government by using his tax-exempt foundation to raise funds that were then used to purchase weapons for the contras.

Channell, who has named North as a coconspirator, was recently interviewed by committee investigators, and some members want to follow up on whether his organization may have targeted Democratic members of Congress who opposed aid for the contras.

At the same time, some members of both committees want a deeper investigation of Central Intelligence Agency complicity in the circumvention of the congressional ban on U.S. military assistance to the Nicaraguan rebels.

The alternative could be to turn CIA matters over to leaders of the Senate and House intelligence committees, whose chairmen sit on the Iran-contra committees. That issue, however, had not been decided as of late yesterday. One source said some CIA officials will be called to testify before the select committees.

The select committee leaders reportedly have not decided on a final list of witnesses for the next round of public hearings, which run June 23-26, with six names under consideration. Two earlier candidates have been postponed until July, according to committee sources. They are Donald P. Gregg, national security adviser for Vice President Bush, and Marine Lt. Col. Robert L. Earl, North's deputy at the NSC who, according to North's secretary Fawn Hall, participated in the shredding of documents on Nov. 21.