Offering humanitarian help for half a century of world crises; Escape to Freedom: The Story of the International Rescue Committee, by Aaron Levenstein. Westport, Conn.: Greenwood Press. 1983. 338 pp. $29.95.

Aaron Levenstein's ''Escape to Freedom'' documents how a relatively small group of Americans and Europeans forged a new structure, independent of church or state, to render assistance to the dispossessed. The agency he describes is the 50-year-old International Rescue Committee (IRC), the offspring of the American-based International Relief Association (with which Albert Einstein was affiliated) and the European Emergency Rescue Committee, both set up to aid those persecuted by Hitler.

From the start the committee's mission ''was not only humanitarian in the Judeo-Christian tradition but also political in the broadest democratic sense.'' Opposed to many of the isms of the period, IRC's secular Samaritans nevertheless had an underlying ideology of their own. ''Freedom'' was (and remains) the watchword, and ''aid to the victims of totalitarian regimes'' - whether ''Black'' or ''Red,'' in the old sense of those terms - the credo.

In some ways such forthright political views set the IRC apart from a number of other voluntary agencies involved with refugees. Its leading spokesman and board chairman for the past 30 years, Leo Cherne, is well known for his vigorous stances and his public statements in favor of aiding those in flight from repressive societies. What is less well known is the extent of his personal involvement in the major refugee movements of our times. ''Escape to Freedom'' describes Cherne's activities and those of the various ''citizens' commissions'' he organized, from the time of the ill-fated Hungarian uprising to the recent crisis in Kampuchea. Levenstein shows the many ways that Cherne, an economist, lawyer, statesman, sculptor (whose work is displayed in the Smithsonian Institution and the Cabinet Room of the White House), and lobbyist is the public embodiment of the IRC.

While Cherne - and Charles (Carel) Sternberg, the executive director - are the most visible representatives of the agency, it is not simply a one- or two-man band. What has been accomplished over the years has been done with the support, encouragement, and active participation of such figures as Charles A. Beard and John Dewey, Elmer Davis and Dorothy Thompson, Harry Gideonse and William Allen Neilson, Angier Biddle Duke and Claiborne Pell, Albert Shanker and William Casey, Mrs. Lawrence Copley Thaw and Irving Howe, John Richardson and Rabbi Marc Tanenbaum, Bayard Rustin and Liv Ullmann. The last two now serve as vice-presidents of the organization.

Early chapters relate how the IRC served the displaced persons of Europe, the Hungarians, the Kurds, the Czechs, the Cubans, the Dominicans, the Haitians, and the Bengalis, the last in an operation run in Calcutta by Levenstein himself. Farther along in the chronology, IRC's activities in Africa are discussed: assistance to those from southern Africa who sought asylum in Bechuanaland (now Botswana), to Biafrans in Nigeria, to Ugandan Asians, and most recently to Ethiopians in Somalia. Levenstein also recounts how IRC workers provided comfort , aid, medical services, job training, and child care to refugees from the People's Republic of China who had escaped to Hong Kong in the days before the entente with the US; to Cubans who made their way to Florida after the revolution; and to thousands of Indochinese, first in Vietnam and later in various countries of ''first asylum'' to which they fled after the fall of Saigon in spring of 1975.

IRC's involvement with Indochinese is particularly noteworthy.

Three months after the end of the war, the agency placed 30 full-time workers in the four American camps set up to facilitate the resettlement of what were later to be known as ''first wave'' refugees from Vietnam. At Camp Pendleton in California, Fort Chaffee in Arkansas, Eglin Air Force Base in Florida, and Fort Indiantowngap in Pennsylvania, while others handled the distribution of food and the provision of medical services, the IRC helped to resettle many individuals and families and to orient them to life in their new homes. By the end of 1975 the job was done. It proved to be but a test run for a much larger endeavor. The boat people were yet to come.

Those who left Indochina in the second wave were a mixture of escapees and expellees, many of the latter ethnic Chinese - people considered both undesirable and exploitable by the new rulers.

As the flood of refugees from Vietnam and Laos increased, so did the resistance of those in the Southeast Asian nations on whose shores they tried to land. Worldwide publicity and the intervention of many governments and private groups led to an international plan to handle the mounting flow of refugees, provide temporary asylum in the ASEAN nations, and aid the refugees in their movement to ''third countries'' like the US. Some 650,000 have already been resettled here.

Long active in many countries of Southeast Asia, the IRC became most visible in Thailand, where, under contract to the Department of State, the agency organized and directed the interviewing and processing of all potentially resettleable refugees from Vietnam, Laos, and Cambodia.

As the Joint Voluntary Agency Representative (or JVAR) in Thailand, the IRC established the largest resettlement office anywhere. It became a model for many similar operations set up by other contracted voluntary agencies in the other countries of the area. It is still engaged in resettlement, and in a myriad of other humanitarian services, from the borders of Cambodia - and Afghanistan and Ethiopia and southern Mexico - to the edges of the Boston Common, where one of its 10 regional offices is.

IRC's chronicler details all this in his review of the agency's activities and in his celebration of its accomplishments. He introduces the reader to IRC's movers and shakers, the programs they devised, and the policies they developed to realize the committee's particular mission.

If Levenstein leaves anything out, it is a sense of the day-to-day tasks carried out by the IRC's field officers and foot soldiers.

While not ignoring them, he says too little about the critical parts played by the middle managers who run the regional offices and the field programs.

He says even less about those in the trenches, the Americans and ''local hires'' employed by or through the agency in domestic resettlement offices or in overseas posts, who do the basic work of the IRC. Their story has yet to be written.

Still, Levenstein's book is a major contribution to understanding international social service and the politics of altruism.

It is also something more. ''Escape to Freedom'' is a well-deserved tribute to a few of the ''just men'' - and women - who have not forgotten that we are all our brothers' keepers.