Drastic reductions in federal aid for housing, food, disability and welfare programs during the Reagan administration have created a nationwide "epidemic of homelessness" that has assumed crisis proportions in the country's largest city, New York officials testified today.

An estimated 100,000 people will pass through the city's emergency-shelter system this year, a 40 percent increase in the number of families and a 30 percent increase in individuals over last year, they said.

New York has the most extensive network of shelters of any city in the nation. But in the last 10 weeks, city officials say, the system has been filled to capacity and hundreds of homeless people, particularly women and children, have been forced to spend nights in the waiting rooms of welfare offices while waiting to be placed.

"Homelessness in the United States has quietly taken on major proportions," said Gov. Mario M. Cuomo, calling for a "well-organized, comprehensive program to provide permanent housing and shelter."

Rep. Ted Weiss (D-N.Y.), chairman of the Government Operations subcommittee that held a field hearing here, said the nation may have 3 million homeless people and that the number is increasing 38 percent a year.

"We have no national commitment to the homeless," he said. "The federal government must take the leading role in ensuring that all Americans who cannot fend for themselves receive emergency food, shelter and medical services."

Congress has yet to address the homelessness issue, Weiss said, except with a $70 million program through the Federal Emergency Management Agency. No comprehensive legislation has been proposed, he said. A much-touted administration initiative to set aside empty federal buildings was "a total failure" and $7.1 million of the $8 million appropriated was not spent on shelters, he said.

Cuomo told the subcommittee that the sterotype of the homeless person as a skid-row derelict or a former mental patient is no longer true. A recent state study found them to be "the unemployed -- people who've lost their jobs -- young or middle-aged, many of them women, a growing number of them with families," he said. "Homelessness today is overwhelmingly caused by poverty, not pathology."

The most basic cause is a severe cutback in federal housing benefits, Cuomo said.

"At its peak, the federal Section 8 program alone which built low- and moderate-income housing supplied $3.2 billion a year to the state's housing market," he said. "This program currently functions on one-third as much . . . . A program that once provided funds for 47,000 households annually, now reaches only 8,000."

"This federal administration has abandoned a 50-year bipartisan commitment to provide housing for low-income people," said Deputy Mayor Stanley Brezenoff.

Since 1981, the year President Reagan succeeded in pushing major budget cuts through Congress, funding for federally assisted housing has been halved.

Overall, George Gross, the city's Human Resources Administration director testified, "since 1981, the city and its residents have lost more than $2 billion in federal aid."

For example, Social Security disability benefits were eliminated for 25,000 residents statewide under new regulations. Up to two-thirds of those affected live in the city.

"Many have lost their homes and have ended up on the streets or in shelters," City Council Chairman Carol Bellamy testified. And, she added that, although a federal court has ordered that thousands be reinstated, "the Social Security administration has avoided compliance with the court order."

Bellamy said federal legislation enacted in 1981 and 1982 made 150,000 city residents ineligible for food stamps. The Omnibus Budget Reconciliation Act of 1981, she said, eliminated 22,000 women and children from federal welfare rolls.

Homelessness has become a major political issue in New York City with Bellamy, a potential candidate for mayor, criticizing Mayor Edward I. Koch's approach to the problem.

Under court order, Koch has increased the city's shelter system by 3,330 beds for single men and 690 beds for single women. Three hundred families are also being housed in shelters, while 2,649 families are put up in dilapidated welfare hotels at a cost of up to $1,200 a month per room because of a drastic shortage of low-cost rental housing.

The city spent $6.8 million a year to shelter the homeless in 1978. This year it will spend $75 million and begin a three-year $64 million building program to develop new shelters. A $43 million housing rehabilitation program has made 3,300 apartments available to homeless families, but the need outpaces the program. In October, housing officials said, the city placed 384 families, but 444 others became homeless.