CHICAGO - Congress' rewrite of the nation's welfare law wrung billions of dollars from the main federal program designed to keep the poor from going hungry: food stamps. Now, four months after the last of $27 billion in food-stamp cuts took effect, evidence is mounting of a large increase in the number of people who can't get enough to eat without help. Surprised and worried by the news, charity leaders and experts on hunger believe the cuts are at least partly to blame. "The economy is booming by most standards we use to measure it, and yet we're saying our demand is up," says Sister Christine Vladimiroff, a Benedictine nun who runs Chicago-based Second Harvest, the nation's largest charity to getting food to the poor. "People come to us because their cupboards are bare," Sister Vladimiroff said. "We don't want to have to say, 'Well, ours are, too."' The U.S. Conference of Mayors released a survey last month that reported average 1997 increases of 16 percent in requests for emergency food _ the largest jump in the 29-city survey since 1992. In addition, the study found 19 percent of those seeking help were turned away, and 46 percent of the cities reported charities and other private programs provided inadequate amounts of food to those helped. Forty-four percent of city officials cited cuts in the food-stamp program as a chief cause of the problem. But many said the blame cannot be placed solely on the changes in the food-stamp program, which reduced the stamps' value, limited to three months the eligibility of able-bodied, childless adults and denied benefits to most legal immigrants. Other, perhaps larger, factors include unemployment and low-paying jobs, they said. For instance, the Weld Food Bank in Greeley, Colo., reported one of the highest increases in the number of people asking for help _ 50 percent _ of any Second Harvest affiliate, but marketing manager Jim Riesberg cautioned against simple explanations. "Sure it's had a tremendous impact, but we can't put everything off on the food-stamp cuts," Riesberg said. "It's too easy." Second Harvest supplies through a network of food banks more than a billion pounds of food a year to soup kitchens, battered women's shelters, meals-on-wheels programs for the elderly and other services for the downtrodden. In an informal survey, Second Harvest found it took an average of 14 percent more food to feed the hungry this November than last. Matthew House, a service center for the homeless in the struggling Douglas neighborhood on Chicago's South Side, sees such statistics played out firsthand. To try to make up for some of what the government will no longer do, the agency is moving from a tiny, crumbling church capable of serving only about 40 "guests" each mealtime to a newly renovated, spacious facility a few blocks away that can handle more than double that. For people like Everton Greenaway, who came to Chicago from Montserrat after the British colony's volcano buried much of the Caribbean island two years ago, Matthew House is a haven. He works at odd jobs to try to make ends meet. But since he is no longer eligible for food stamps, Greenaway often winds up there for meals. "I might be down, but I always remember that they respect us and love us," he said after a recent breakfast. Thirteen states have moved to keep food-stamp benefits intact for some legal immigrants by spending their own money _ ranging from $2.1 million in Maryland to $65 million in Washington state. Forty-two states and the District of Columbia have received waivers for the cutoff of childless adults in areas of high unemployment. No state has made up for all the cuts, which resulted in a drop in the number collecting the average $71-a-month benefit from 25 million in September 1996 to 21 million a year later. Almost a million of those are legal immigrants who had either not served in the U.S. military, worked 10 years in the United States or been granted asylum. Second Harvest and groups including the National Council of La Raza, the Jewish Federation and Catholic Charities are lobbying to get President Clinton to push in his Jan. 27 State of the Union address for renewed access for legal immigrants. They want him to include the same stipulation in his 1999 spending plan to be unveiled Feb. 2.