Forty-four countries have joined the United Nations Children's Fund in a high-visibility save-the-children campaign and many expect to halve their child mortality rates as a result, Executive Director James Grant announced today in UNICEF's annual "State of the World's Children" report.

More than a million children's lives have been saved in the past year, the report said, and the success of these pilot efforts, Grant said in an interview, make it clear for the first time that "one could expect by 1990, if these programs are universally applied, to save the lives of about half of the 40,000 children who now die each day in the developing world."

The methods of achieving this goal are basic:

*Inoculation against six diseases (measles, tetanus, whooping cough, polio, diphtheria and tuberculosis) that now kill 3.5 million children a year.

*Teaching parents how to administer oral rehydration therapy (a mixture of water, salt and sugar) to treat the bouts of diarrhea that now kill 4 million children a year.

The health technology to achieve these goals includes consistent vaccinations, "cold chains" of refrigeration that reach into remote parts of the Third World, and cheap, plentiful and easily used packets of oral rehydration mix. All this has been available for years but has been "underutilized," Grant said.

The political idea that put the technology to work emerged during a seminar three years ago involving UNICEF, the U.S. Agency for International Development and other U.N agencies such as the World Health Organization, Food and Agriculture Organization, U.N. Development Program and World Bank. Grant is careful to give credit to all these agencies, which have now banded together in a joint "task force for child survival."

At that seminar, Grant said, there was a "magic moment" when the participants grasped that the only way to reach the poorest Third World parents and convince them to try immunization and oral rehydration therapy was to mobilize all elements in a society -- political leaders, religious and social organizations and the mass media. And the way to start, it turned out, was for Grant to go right to the top in each country, bypassing the normal channels of the health ministries.

President Belisario Betancur of Colombia was his first target, and he responded with enthusiasm. But it wasn't until a second session in November 1983 that Colombia's machinery was fully mobilized, the political opposition was brought in, and the campaign became the showpiece of the international crusade. Child deaths there were cut from 60,000 a year to 30,000 after a 1984 vaccination effort raised the nation's child immunization rate to 75 percent.

That, Grant noted, is close to the 80 percent target for achieving critical mass, the point at which "if one kid gets measles, it's like a golf ball hitting a sand trap; phht, it stops."

Some countries, such as Bolivia and Ecuador, embraced similar programs through efforts by UNICEF regional directors. In Burkina Faso, Grant said, government leader Capt. Thomas Sankara "became enthused on his own, after reading our 1983 report. Our biggest problem was to slow him down."

Other leaders took more selling. This was aided by a letter last June from U.N. Secretary General Javier Perez de Cuellar to all heads of state or government, and the United Nations' 40th anniversary fete two months ago, which brought more than 100 leaders to New York and produced a number of commitments, including one from Bangladesh, the last of the big-population countries to sign on.

Grant concedes that the major tests are still to come: the questions of sustainability (as the next generation of children emerges) and universality. In Colombia, Betancur is trying to build sustainability into the process by revamping the country's educational curriculum to include preventive health measures, and by requiring all high school students to perform 100 hours of national health service.

Because the effort is linked to the personal prestige of national leaders, Grant said, "there is a danger if they leave the scene abruptly. I had my fingers crossed after the coup in Nigeria earlier this year. It was a major test for us." But the new leadership promptly embraced the program.

Grant said he found that political leaders had no problem taking to the idea because "the payoff for the government is there and is relatively high; you get rather quick results at low cost." The highest resistance has come from the medical community, which in many countries "is not used to outreach; they fear the loss of their mystique."

The cost of universal Third World immunization would be about $500 million a year, until the program achieves a sustaining pattern and costs drop. The agencies involved have enough to finance programs, but with more recipient countries coming on board "we will hit the financial crunch in 1986 and will fall behind, unless donors come up with at least $150 million over 1984 contribution levels," Grant said.

So far, Italy has been the most responsive, offering to pay not only external costs but part of the local costs (for vehicles, health workers, refrigeration) for the 26 nations hit by the African food emergency.

Grant admits that the African emergency operations have put a crimp in his child survival crusade in the nations involved and limited the use of resources and expertise in other regions. But he insists that the problems have been largely logistical rather than political.

"The last year has shown a greater willingness by governments to see immunization and oral rehydration therapy programs cross borders of conflict than food programs," he said. "Afer all, vaccines are of no use to soldiers." He cited as examples El Salvador's immunization campaign during "days of tranquility" when the fighting stopped and a less well-known agreement by Uganda to permit airlifts of vaccine into rebel-held areas.

Grant was reluctant to point a finger at governments that had not responded to his drive, but the report released in Washington today shows that Mexico, Iran, Zaire, Angola and the Philippines are among the nations not yet enlisted.

For the most part, Grant started his campaign among the most populous countries. In India, Prime Minister Rajiv Gandhi declared the nationwide immunization campaign a "living memorial" to his late mother and predecessor, Indira Gandhi.

China, skeptical at first, was finally convinced by a sales pitch to the top leaders this August. Grant was born there in 1922, and both his father and grandfather did public health work in China.

Grant served in the Far East during World War II ("I walked from India to Burma as we opened the Burma Road"), worked on the staff of Gen. George C. Marshall in his futile attempt to reconcile the warring factions in China, and then worked in China with the U.N. Relief and Rehabilitation Administration. After a long career in the U.S. foreign aid agency that took him to Sri Lanka, Turkey and India, he headed Washington's nonprofit Overseas Development Council from its inception in 1969 until he took over at UNICEF in 1980.

The agency he inherited from Henry Labouisse already had the mission of helping the world's children and mothers, the access to voluntary funding that went with that calling, and the reputation of being lean and efficient.

Grant recalled that in the late 1940s the United States wanted to phase out UNICEF after it did its emergency work in wartorn Europe. It slowly started working in the Third World, functioning "primarily as a symbol." In the late 1970s, Grant said, UNICEF "took on a larger conceptual role," promoting a philosophy of development that included basic small-scale services such as village health workers and "appropriate" technology that could be immediately useful to the poor.