WASHINGTON, May 26--President Truman today asked Congress for authority to arm, equip, and train the armed forces of western hemisphere nations, including Canada. In a special message, he told the legislators that "world developments" have made such action "more important" than when he asked similar legislation a year ago.

One key aim of the program is to bring about standardization of arms and military methods throughout the western hemisphere so that forces of all the nations can co-operate more effectively in defense of this part of the world.

The program is identical with a bill approved last session by the House Foreign Affairs Committee at the President's recommendation but which failed of passage.

Including Canada in the western hemisphere arms standardization proposals, Mr. Trunian said that the British Dominion's "cooperation with the United States in matters affecting their their common defense is of particular importance."

The bill President Truman asked of Congress today would authorize this government to:

1. Train soldiers, sailors and airmen of other American states. The training may be given at schools in the United States.

2. Maintain and repair the other countries' military equipment.

3. Transfer to those countries U. S. arms, planes, ships and other military items, plus technical information.

4. Accept in payment any sort of benefit, direct of indirect, which the President may find satisfactory.

5. But up from such countries any war goods they may have which do not fit into the plan, crediting the price against advances made by the United States in connection with the project