Colbert I. King, American executive director for the World Bank since December 1979, has resigned his post effective March 31, warning in a letter to President Reagan that "now is not the time to undermine our influence in the World Bank and global economic development."

The Reagan administration has indicated in a number of ways that it intends to reexamine its commitment to the World Bank and other multilateral institutions and, where possible, to favor bilateral aid over multilateral assistance.

Deputy Treasury Secretary R. T. McNamar told a House Banking subcommittee Wednesday that while the Reagan administration will honor certain international financial commitments made by prior administrations, it would stretch out the payments and agree to no new undertakings until a thorough cost-benefit review of U.S. participations is completed.

King, a Carter holdover, had agreed to stay in his post until a successor was appointed. But two weeks ago, he was instructed to pass on to the World Bank executive board the Reagan administration's decision not to support a new bank affiliate to generate oil and energy projects in the Third World.

King wrote the president that he hoped the now well-publicized reexamination of the U.S. role in all of the institutions would conclude "that it is absolutely crucial for the United States to continue its strong support for the World Bank."

In an impassioned statement to the board of executive directors on Tuesday, King said the bank faces "a critical juncture" and raised the question whether the executive directors, as officers of the bank, could continue to reflect merely the views of their sponsoring governments.

"It is to us, especially during the upcoming months, to recognize and detect stresses which can threaten the bank, whether these stresses are caused by our governments or by the manner in which we conduct business here. It is in these moments of great stress when we must place the interests of the bank first and say to each other if we must -- and even to our governments if necessary -- 'Enough. There are certain limits,'" King said.

He added his hope that the United States "will continue to pursue its historic role in the bank," which he said implies a commitment to a belief that "dignity and self-fulfillment should be placed in reach of everyone."