MANILA -- Four Peace Corps volunteers working in the rural Philippines described their experience as the most physically and mentally trying times of their lives, testing their mettle in a way none of their training could have prepared them for.

All of them came away greatly disturbed by the depth of this country's rural poverty.

"I can't believe how tough life is out there," said Gregg Baker, 26, who once did volunteer work for CARE in Chicago.

"It's very hot. It's a little bit lonely. Maybe you're hungry because all you had for breakfast was salted fish. I just don't like hot weather, and after two years, I don't think I ever adjusted to it."

The four volunteers interviewed here had differing reasons for joining the Peace Corps.

Baker, who has done graduate work at the Fletcher School of Law and Diplomacy, hoped the field work would help him find a job in international agricultural economics.

David and Barbara Oltman, fundamentalist Christians, believed their religious convictions required it.

Jennifer Clark, 45, a former secretary at the University of California at Los Angeles, said she "was profoundly bored . . . and needed a complete change."

All four said they were primarily eager for a change. They got it.

Clark remembers her visit to the room that would become her home for two years.

"There were flies all over my room and there were red ants on the toilet that bit when I sat down," she said. "It was like living 400 years ago."

Given such hardships, there are, of course, doubts and second thoughts.

The first great wave of anxiety comes when the worker first sees his site, the place he will call home for the next two years of his life. Those first weeks are hardest.

"Many times I thought, 'What am I doing here? When will it be over?' I can't say I didn't get bored eating rice and fish for two years," Clark said.

Asked if he ever wondered why he had come, Baker replied, "every day." He said he thought of quitting after only a week, but was talked out of it by a senior counselor. After the first few months, he said, it becomes a challenge to stay and complete the tour.

"A couple of times it crossed our minds to leave," said David Oltman. "We would ask ourselves, 'What are we doing here? What is our purpose? Are we really accomplishing anything?' "

Marriage brings benefits like companionship. But the Oltmans said they discovered that marriage brings unforeseen problems.

"Peace Corps tends to make or break a marriage," David Oltman said. "If it works, nothing else bonds you together like it."

"You see this person 24 hours a day," said Barbara Oltman. "Plus, you see this person stripped of everything; you have no skills out there." The Oltmans discovered new sides to their personalities, like David's intense competitiveness with his wife when he discovered that she was becoming more fluent in the local language than he.

The Oltmans said the greatest hardship was the pressure of the job, the feeling that they were not producing great and lasting projects that would change the life of their village. There is an inevitable sense of failure, and then the realization that sometimes small-scale projects can make a small-scale contribution.

The Oltmans were assigned to work with members of the Ati tribal minority in a tiny barrio on Panay Island in the central Philippines. David taught mathematics while Barbara began a literacy course. They also helped the Ati build a day care center and plant new crops.

"I thought I should have had a bigger project, doing something in food production," Barbara Oltman said.

Clark, a one-time reporter for the Evening Outlook in Santa Monica, Calif., was assigned to a town 13 miles from Iloilo City, also on Panay. She started a feeding program for the two-thirds of the children in her barrio who were malnourished. She also started an antirabies program, an eye clinic and a day care program.

"The first week is the hardest," she recalls. "It takes a long time to find your work."

Baker was a rarity. He had one of the few Peace Corps development projects here that seemed clearly to succeed in a big way.

Assigned to Mabini on Bohol Island, Baker helped develop the town cooperative from 72 members to 170, and the co-op has now branched into marketing, credit, storage and processing for the town's rice crop. He helped the village apply for a small U.S. AID grant to construct two rice blowers, and a new rice scale, so the farmers could weigh their crops themselves instead of relying on the "tilted" scales of dishonest traders.

He also helped form a federation with 14 other nearby cooperatives to give co-op presidents a chance to meet and exchange views. He also helped start a fertilizer loan business, complete with crop insurance, and a model farm on old pasturelands to demonstrate techniques for growing vegetables and other new crops.

"That was the shocking thing," he said. "This is what I wanted to do, agricultural economics."

Some of the volunteers, as they come near the end of their tours here, expressed concern about the future, their marketability in the search for a job, and their ability readjust to life at home.

"I have a lot of anxiety; I finally get all cranked up, and now its almost time to leave," said Clark.

Clark was unusual in one respect. She visited the United States halfway through her tour to attend a sister's wedding. "It was such a culture shock," she said. In her barrio, she said, "Children just don't have toys . . . . But in California, the toy Mercedes, the RVs; it's amazing."

Baker said; "I want to have an impact on U.S. policy in developing countries. There are many ways to do that. It can be through a bank, it can be through international organizations.

"Now I've seen it is possible for one person to make a difference."