WASHINGTON — President Bush approved an order today that rewrites the rules governing spying by American intelligence agencies, both in America and abroad, and strengthens the authority of the national intelligence director, according to an American official and government documents.

Executive Order 12333, which lays out the responsibilities of each of the 16 agencies, maintains the decades-old prohibitions on assassination and using unwitting human subjects for scientific experiments, according to a power point briefing given to Congress that was reviewed by The Associated Press. The CIA notoriously tested LSD on human subjects in the 1950s, which was revealed by a Senate investigation in 1977.

The new order gives the national intelligence director, a position created in 2005, new authority over any intelligence information collected that pertains to more than one agency — an attempt to force greater information exchange among agencies traditionally reluctant to share their most prized intelligence. The order directs the attorney general to develop guidelines to allow agencies access to information held by other agencies. That could potentially include the sharing of sensitive information about Americans.

The order has been under revision for more than a year, an attempt to update a nearly 30-year-old presidential order to reflect organizational changes made in the intelligence agencies after the September 11, 2001, terrorist attacks.

It was carried on in secret in the midst of pitched national debate about the appropriate balance between civil liberties and security, spurred by the president’s warrantless wiretapping program.

The briefing charts assert that the new order maintains or improves civil liberties protections for Americans.

Interest in the rewrite inside the 16 agencies has been high because it establishes what agencies’ powers and limitations will be.

The order, which has not yet been publicly released, is expected to cut into one of the CIA’s traditional roles. The CIA has for 50 years set the policy and largely called the shots on relationships between American intelligence agencies and their foreign counterparts. According to the briefing charts, the national intelligence director will now set the rules for engaging with foreign intelligence and security services. The CIA will now just “coordinate implementation,” according to the briefing charts.

The order also gives the national intelligence director’s office the power of the purse: It was granted the authority to make acquisition decisions on certain national intelligence programs. It is also updated to include the national intelligence director and two major defense spy agencies — the National Reconnaissance Office, which operates spy satellites, and the National Geospatial-Intelligence Agency, which analyzes imagery. It did not explain the FBI’s domestic intelligence mission, which has gotten increasing attention since 9/11.