The United Nations World Food Program has begun cutting its aid to North Korea because of a shortfall in donations, and officials say millions of children and pregnant women will go hungry soon.

Since May, the United Nations has warned that shrinking donations will force its World Food Program to cut aid to millions of North Koreans this year. Now, as winter approaches, the cuts have become a reality.

Rick Corsino, country director for the World Food Program in North Korea, said the most vulnerable population will be hit the hardest. "We've been operating there for six or seven years, since late 1995, and this is the very first time that we've actually had to make serious cutbacks in our distribution plans, mainly the ones aimed at the feeding of the most vulnerable core beneficiaries, and these are of course the youngest children, and pregnant and nursing women," he said.

The shortages will affect three million people over the next two months, mostly in North Korea's relatively better-off southern and western provinces. In addition, 1.5 million in the east face shortages early next year.

The United Nations has phased in the aid cuts. This month it cut food aid to primary and secondary school children. In October, the agency will reduce food to kindergartners and pregnant and nursing mothers. Contributions to nursery school children will be cut in November.

Mr. Corsino said because many of North Korea's hungry are so young, the damage from the drop in aid will be irreve rsible. "If we're not able to provide food to these groups, then you see permanent damage," he said. "This is both physical damage and impaired learning. And this damage is irrecoverable."

Nearly half of all North Korean school children under age five are malnourished, while an additional four million are severely underfed, which leaves many of them physically and mentally underdeveloped. About half-a-million pregnant and nursing women are also poorly nourished.

The World Food Program reaches roughly one-third of North Korea's total population. But distributing aid takes time, and the United Nations says that even if additional contributions come now, it would be two months before the food got to recipients. If new donations do not come, the United Nations says it will have to shut down its North Korean food operations completely within a few months.