ROME (AP) _ Swarms of locusts migrating from northwest Africa will threaten harvests in 15 African nations and it will require about $300 million in aid to make up for damaged crops, U.N. officials said Friday.

''There is actually little hope of being able to contain the plague in the near future,'' the director-general of the U.N. Food and Agriculture Organization, Edouard Saouma, said in a statement.

Saouma said the invasion was ''of unprecedented dimensions'' and will move through the sub-Sahara region to ''affect the food security of 15 African countries, from the Atlantic Ocean to the Red Sea.''

Dr. Lukas Brader, head of the Emergency Center for Locust Operations at FAO, said the insects moved south in April and May, earlier than expected, because plentiful rains there resulted in favorable breeding and living conditions.

He said the situation will worsen during the next few weeks as new swarms arrive, coinciding with the harvest in the Sahel, the area that extends from Senegal to the Sudan and separates the arid Sahara from tropical West Africa.

Brader said countries in this region face a potential loss of 1 million tons of grains. About $300 million worth of food aid would be required to make up for the destroyed crops, he said.

U.N. experts have said a swarm covering just half a square mile can contain 50 million insects, weigh 100 tons and eat its weight in vegetation each day.

Brader said that Morocco, Algeria and Tunisia, which were first infested with the locusts, had succeeded in keeping the insects south of the Atlas mountains, in relatively uncultivated areas.

He added that since Jan. 1, 12.3 million acres in those countries and Mauritania have been treated with pesticides.

In the Sahel, locust control is more difficult because the insects are more dispersed.

Saouma said in his statement that locust swarms were sighted in Sudan this week and that ''it must now be feared the plague will extend to the Red Sea, where it may invade the Arabian peninsula and the horn of Africa.''

If unchecked, the swarms eventually could reach Israel and Turkey as well as the Indian subcontinent.

Authorities try to control locusts mainly by spraying pesticides.

The fight has cost $45 million so far this year, and the organization estimates a total of $150 million may be needed for the year.

The last major invasion of locusts in Africa began in 1950 and lasted for 13 years.