A LONG with the color slides, the gaunt look, and the native sandals, Peace Corps volunteers return home with a little piece of emotional baggage.Whether stamped "Ghana" or "Guatemala," the baggage contains the elements common to every third-world experience: the cooking-fire odors that conjure memories as vivid as any photo; the wide smiles that polish the disappointing edges off the inevitable cultural misunderstandings; and the Janus of joy and despair that guards each day there. What to do with this baggage when the volunteers return home has meant equal parts frustration and fulfillment for them over the years. It is the fresh-faced, can-do imagery of the departure of volunteers that has captured the imaginations of young Americans since the Kennedy Camelot years when the Peace Corps was created to help developing countries meet trained manpower needs and promote a better understanding of Americans abroad. But that has largely overshadowed the return of volunteers and the Corps' lesser-known third goal: to help promote American understanding of other nations. As the Peace Corps celebrates the 30th anniversary of its congressional authorization this month, the returned-volunteer population has swelled to more than 125,000. They are represented throughout society - most noticeably in the foreign service and the international development community. And for the first time, a returned Peace Corps volunteer - Paul Tsongas, former US senator from Massachussetts - is running for president. "The agency has been enormously successful overseas. But there is an equally broad consensus that the third goal has never been achieved," observes Paul Coverdell, director of the Peace Corps since 1987. Without formally integrating volunteers' experiences back home, volunteers often say the return to the US is as much a culture shock as the immersion in a foreign country was. Whenever former volunteers gather - as they have been this summer in anniversary reunions around the country - there is the bittersweet confirmation that in a nation that has trouble even finding itself on a map, volunteers are best understood among themselves. At a recent 30th anniversary celebration here, the Monitor interviewed Peace Corps veterans about the agency's third goal. Their experiences say as much about where they've been as where Americans are in the world. FOR Larry Leckenby (Colombia, 1963-65), it took 20 years even to recognize the nearly debilitating inner conflict he had reconciling the simple roots of his Peace Corps experience and the complex American life he returned to. "My life was permanently changed. Yet there was nothing in our culture that deals with that profound change in a peacetime, noncombat situation," he says of the frustration he felt not being able to get friends to share his interest in the third world. "When you've seen people hungry all the time and you're eating all the time, it creates a split in your consciousness and it's difficult to express," says Mr. Leckenby. Bouncing between careers in counseling the homeless and prisoners and selling Volkswagens and boats, Leckenby had his first contact with volunteers since his return at the 25th Peace Corps reunion in 1986. Most volunteers experience this conflict to some degree. Leckenby, whose job now is hosting third-world visitors, says despite the hunger and despair in Latin America, there is a basic familial happiness there that Americans, "whose time spent together is little but anxious middle-class comings and goings," can learn from. He says it is imperative that Americans "know something about the third world, because that is to know something about our country's future. They are coming to us and bringing their economic poverty to us." KITTY THUERMER (Mali, 1977-79) suggests many return volunteers "almost can't bear to look back." Recounting their experiences is often hard to do. But, says the former public-health worker in a Sahel village, American insensitivity to the third world is not deep-rooted. "Peace Corps volunteers are often frustrated because they think no one's interested. After you explain your war stories, they ask you if you know who won the latest Celtics game, and then you feel completely out of it," observes Ms. Thuermer, now a communications officer for Appropriate Technology International here. "Americans are not insensitive on purpose. The insensitivity comes from a lack of exposure to things normal, positive. If something international touches their lives, they will care about it," says Thuermer, who wrote a 100-page unit on Africa in a global studies textbook. War often shapes the American image of foreign people, she says. When the overseas experience is shaped by peace, not war - by foreigners as friends, not foes, she says, "We refuse to accept stereotypes about foreign people. It can convince people about the common humanity [between cultures] ... that my neighbor was not some pinup in National Geographic but Fanta, my neighbor who taught me how to pound millet." PAUL TSONGAS (Ethiopia, 1961-1963) says, "The worst year of my life was my first year back.... When you come back, no one wants to talk to you.... I felt like emotional flotsam." But his two years building a school in rural Ethiopia and then teaching in it galvanized his career, says the former US senator and current presidential hopeful. "I went to Ethiopia a Republican, and returned a Democrat. "My life has been an attempt to feel about myself the way I did then," he says. "The strongest contribution of a Peace Corps volunteer is to the United States of America." But Mr. Tsongas is pragmatic about the third goal, adding that "awareness and understanding are two different things. You can know about [hunger and poverty], but you can't feel it ... you can't artificially bring it to Americans. You're not going to get 250 million Americans to have an overseas experience." He calls Peace Corps volunteers the vanguard, and says that "it is always the vanguard that will define [foreign] policy," he says, gesturing toward the Vietnam Memorial not far from where he's being interviewed. "That vanguard has to grow and become more aware, because when you make a mistake based on miscalculations of how people think in the third world, it's your sons and daughters who will be memorialized."