Isabel Snow is nearly out of breath as she trudges up three flights of stairs to the Arlington apartment, she shares with four of her six children and a granddaughter.

Snow has just come home from work, and as she nestles wearily into the corner of the couch, she wonders if she will soon have to work seven days a week, maybe even double shifts, to clothe and feed her family.

Snow is on welfare, a system she despises but has depended on for 12 years. "I cannot make it off welfare, plus sitting around all day would drive me crazy. I've got to work," she says. "I feel a lot of people (on welfare) can work and are just too lazy to. You should get out and go to work if you're able-bodied. Everybody should do an equal share."

As a part-time home health aide, Snow brings home about $3,800 a year. She also receives a total of about $4,000 a year in food stamps, in Aid to Families with Dependent Children (AFDC and in other government aid. But Snow, who is 40, is afraid Ronald Reagan's proposed cuts in food stamps and other social service programs will significantly alter her life.

"I just have a feeling I will be cut off," she says. "They always feel if you're working, you don't need (financial help) as bad as the people who aren't working."

The cutbacks proposed by Reagan are expected to affect every facet of the social welfare system -- from food stamps to AFDC to school lunch programs.

The SNOWS, like many poor families, benefit from nearly all those programs: For example, Snow receives about $240 monthly in AFDC and $83 in food stamps. Her three school-aged children receive free school lunches, and this winter, she received a $160 fuel assistance allotment. Her 21-year-old handicapped daughter and 2-year-old granddaughter also receive federal aid that is not counted in calculating the family's benefits.

Under current Reagan proposals, Snow is unlikely to lose all her benefits. For instance, Reagan has proposed that food stamps go only to families whose gross income is less than 130 percent of the official poverty level. For a family of four, that means annual income could not exceed $11,000, compared to the current limit of $14,000.

But even a family like the Snows, whose gross income is expected to fall well below the proposed limits, there could be some cutbacks. For instance, families whose children receive free school lunches would lose some food stamps benefits.

Last month, 2,903 Arlington families, or 5,284 individuals, received food stamps. Another 827 families, or 2,032 persons, received funds from the federal Aid to Families with Dependent Children program. Arlington distributed nearly $2 million worth of food stamps last year and nearly $3 million in AFDC funds.

Last year, Fairfax County distributed nearly $9.4 million in AFDC funds to 7,294 people, or 2,639 households, and nearly $5.3 million in food stamps to 12,843 people, or 5,168 households. In Alexandria last year, the city disbursed nearly $3.4 million in food stamps to 6,955 people, or 2,959 households, and $4.2 million in AFDC funds to 4,150 people, or 1,440 households.

Among groups in Northern Virginia that work with poor families, the reaction to the Reagan proposals has been one of apprehension. Already, directors of social service agencies and school lunch programs have begun meeting to discuss the possible impact, and what, if any, recourse they might have. They are particularly concerned about the potential effects on such programs as foster care, daycare and companion services for the elderly.

John Robinson, director of the Martin Luther King Center in the predominantly black Nauck section of Arlington, said he has heard cries of concern from the poor all over the county. "Everywhere they go, even in restaurants, people are upset because the government is spending so much money on moon shots and can't take care of the people on earth . . ."

Reagan officials have estimated the total cutbacks in social welfare programs could save billions of tax dollars. The food stamp proposal alone, according to the Reagan administration, could save $1.8 billion. But there is considerable skepticism among area officials that the final program adopted by Congress will be as severe as proposed.

Barbara Glasser, director of social services for Arlington, cautions that it is "far too premature" to predict the proposals' impact. Glasser said her department has no way of knowing, until Congress acts, how many persons would be affected by the cutbacks.

Martin Wasserman, director of Arlington's Department of Human Resources, also was cautious about early predictions, but he said, "Given the magnitude (of the proposed cuts), it's inconceivable that the poor and 'truly needy' won't be adversely affected by the reductions.

Like the counterparts, Wasserman is worried about the ability of state and local governments to bridge the financial gap left by the loss of federal funds, and he hopes local jurisdictions will have a "reasonable lead time to develop creative alternatives" to aid the poor who may lose benefits.

Wasserman also contends that the predicted savings may be a bit like robbing Peter to pay Paul.For exmple, Wasserman contends that the proposals will increase paperwork and administrative overhead, diverting money from services to the poor.

"They need to give us money with fewer restrictions," he added. "I'd like to see X number of dollars go to the department and let us establish the priorities."

While area officials await the outcome of congressional action on the Reagan proposals, the people who will be most affected by the cutbacks, people like Isabel Snow, already are planning for the worst.

"I'll probably have to work seven days a week to make ends meet and stop spending as much time with my family as I'd like." Snow says. "And it'll probably mean a lot of meatless meals. And if I have to buy clothes for the children, I'll probably have to cut the food short."