It's called the ''Mego'' factor - and it's increasingly worrying United Nations, United States, and third-world officials who are urgently concerned about the future of mankind.
''Mego,'' a piece of shorthand from experts in the news media, stands for ''my eyes glaze over.''
It describes, officials say, the reaction of far too many readers and viewers in the richer one-third of the world when told that the population crisis is still urgent, and in many areas is growing worse.
The developing world grows by 1 million people every five days.
Despite some successes in China, Thailand, Indonesia, and Mexico, 80 million people pour into the world each year, 73 million of them in poorer African, Asian, and Latin American villages and slums. Food supplies, land, water, schools, housing, job opportunities, and more are under severe strain in Africa, in particular.
There are 500 million couples of child-bearing age in the third world. Global population, 4.6 billion today, will reach 6 billion by the year 2000 and almost 11 billion by the year 2025 unless fewer children are born, UN experts argue.
It is not that richer-country citizens are unconcerned, the officials say. But they have heard the message so many times, couched in abstract percentages, that they lose sight of the human urgency and drama behind the figures.
Communicating the message is vital, officials say, if more financial aid is to be given, especially by the United States, the world's largest donor. Family-planning aid ($240 million in fiscal 1984, ending Sept. 30) is under fire in Washington from vocal right-to-life groups that have persuaded the Reagan White House to tighten aid rules in this election year.
Thirty-one delegates from 18 countries met recently in Drammen, near Oslo, to tackle the communications issue at a United Nations population seminar. It was a follow-up to the second world population conference attended by 148 nations in Mexico City Aug. 6 to 14.
Among its ideas: (1) setting up a major prize for journalism on population issues, (2) declaring a UN population day to give the media a new event on which to peg coverage, (3) educating editors who assign coverage with more and better background seminars.
''Our main problem is sustaining public interest for the next 10 years until the next world conference,'' said Raphael Salas, the man who organized the Mexico City gathering.
Mr. Salas, executive director of the United Nations Fund for Population Activities (UNFPA), added that people should not be less concerned because world population growth rates fell from about 2 percent a year to about 1.7 percent in the last decade.
''Absolute numbers are still rising fast,'' he says.
Pranay Gupte, whose book ''The Crowded Earth'' has just been published in New York, said, ''Population is a hard story to sell because it is gradual. It's not dramatic, not explosive....''
Headlines generated worldwide by the Mexico City conference owed a good deal to the controversial election-year stand of the US, which almost alone among delegations tried to downgrade family-planning aid in favor of free-enterprise economic growth.
Recent interviews in 10 countries unearthed the following efforts to bring the message home:
* ''If I go to India and I am asked how many children I have, I reply one hundred,'' said Arne Fjortoft of Norway's Worldview International Foundation, in Drammen.
''Actually I have two, but they consume the same resources in a year that 100 children in India do....
''Norway produces fish meal with enough protein in it to feed 70 million people a year, but ... 40,000 children die of malnutrition in the world every day....''
* In Sri Lanka, a prominent population worker also put it all in terms of food:
Two years from now, just one of Sri Lanka's 25 districts will require, every day, 31,000 more coconuts, 46,504 more eggs, and 2.8 million more gallons of water than it did in 1982.
Brig. Denis Hapugalle, who worked out the figures using standard army units per day per capita, said in Colombo that ''you must talk in practical terms, and not over people's heads.''
* ''In many countries, fully half the population was born since Lyndon Johnson (was elected) President of the US in 1964,'' says Dr. J. Joseph Speidel, vice-president of the Population Crisis Committee in Washington.
Dr. Speidel says that outside China only one-third of the 500 million couples in the third world ''have any ready access to services, and only 21 percent are using contraceptives.''