The plethora of restaurants in Old Town Alexandria can satisfy any palate on almost any budget, but nearly every night now, the longest lines at dinner time are at an old brick building on South West Street, on the fringes of the affluent old sector.

There, in a converted grocery store, nearly 50 people gather around 5:30 each evening for a hot meal that may be the only one they eat that day. More important to them, it's free.

Reminiscent of the "soup kitchens" of the Depression, the meals are provided by Christ House, a department of Catholic Charities and a United Way agency, with the aid of church and charitable groups from Northern Virginia. The house also is a 14-bed, temporary shelter for those who have nowhere else to go.

On most nights now, the beds are filled.

Christ House is just one of dozens of local organizations experiencing an increase in requests for help from the temporarily and perennially downtrodden.

From small groups to large -- from AMEN (Arlingtonians Ministering to Emergency Needs) and FISH (For Immediate Sympathetic Help) to the Salvation Army, Catholic Charities and the Jewish Social Service Agency -- Northern Virginia charities expect their caseloads to grow heavier in January and February because of a rising unemployment rate and further budget cuts, particularly in social service programs.

They've begun stocking "food closets" with nonperishable goods to help tide over the needy for a few days. For the longer term, they are raising money for food vouchers redeemable for meats and other restricted goods, such as baby foods.

Food, however, is not always the item most in demand. Charity representatives say they often need money to help people facing eviction or loss of heating pay their rent or utility bills. They also help buy medical supplies no longer covered by Medicaid.

Charities spokesmen say it is no longer unusual for laid-off government workers to walk through the door, seeking job referrals or temporary work.

In the past, much of the money for such forms of assistance has come from the United Way, but officers of the organizations say they expect they will have to rely even more on the private sector next year.

"I think we're going to have an increase in business," said Ted Ostrom, director of Christ House. "Just this month, we're starting to see people we haven't seen before, and I imagine some of it is due to budget cuts, program cuts and rising unemployment."

Most of the people who come to the house for evening meals are trying to scrimp on their food budgets to save money for rent, Ostrom said. If a person comes more than 12 times a month, though, a staff member will try to counsel him and determine if, for example, he's eligible for food stamps but hasn't applied, he said.

Those seeking shelter -- a maximum of three weeks' lodging is permitted -- usually are people who have lost their jobs and have been evicted for nonpayment of rent, he said.

Capt. Dewey Alderson of the Fairfax County Corps of the Salvation Army estimates that 10 percent more people have asked for help this year than last, primarily for utility and rent money. This fiscal year the Fairfax Corps expects to spend $286,000 on programs other than its child-care center, roughly $30,000 more than last fiscal year, Alderson said.

Because the county is so affluent, he said, "things haven't gotten that rough out here yet, but I'm afraid it's heading that way."

In Arlington, however, the Salvation Army has seen a "significant increase" in requests for help over the last few years, especially as the county's large immigrant population has grown, said Capt. Tom Overton, who runs the Arlington Corps.

Overton said the Army helped 46 people in January of 1979 and 124 in January of 1981.

Overton said the local corps spent almost $227,000 in fiscal 1981 on food, clothing, and rent and utility-bill assistance. This year, he estimates, it will spend almost $238,000 -- or much more if donations keep pace with increased needs.

"It remains to be seen what's going to happen if everything gets as bad as people say it will," Overton said. "I expect a significant increase (in requests for help). . . . It's going to be interesting to see how we fare with what's happening in the government.

"I have a feeling that, because of the way the economy is going, the general public is going to become more aware of private agencies such as ours. I hope it's going to result in an increase of support. It's going to have to if the private sector is going to take up the slack."

Nancy Murphy, supervisor of the emergency assistance program for Catholic Charities in Northern Virginia, said they too are getting more requests for food and rent assistance.

In July, she said, Catholic Charities gave financial aid to 55 persons and food to another 83. By October, those numbers had risen to 86 recipients of money and 100 who received food.

"None of it really reflects the (federal) budget cuts yet because they didn't start until October," Murphy said. "But we're finding more people are getting laid off from a variety of jobs.

"A lot of people were coming to this area thinking it was recession-proof, that they could get jobs in Washington, D.C., where the streets were paved with gold."

Catholic Charities, supported by the United Way, the diocese and individual contributions, wants to boost its operating budget, Murphy said. "Hopefully, we'll get more this year than last," she said. "But people who gave last year may have been laid off or are afraid they're going to be, and may not give as much."

Janis Colton, coordinator of services for the Jewish Social Service Agency in Northern Virginia, agrees: "We are dependent on the public, and if inflation continues and if people can't give as they did, the volunteer organizations are going to be getting it two ways. We'll be getting increased requests, but our resources won't be as great."

Colton said her agency is more involved in counseling than in financial aid, although occasionally it has given rent subsidies and emergency food supplies. She said the counselors often refer people to public and private programs, such as the Christ House shelter, which is nonsectarian.

She added that contacts between public and private charities have increased recently, in anticipation of heavier demands on both next year.

In Arlington and Fairfax counties, the Salvation Army runs a clearinghouse to help charity groups coordinate their efforts. The names of those who request aid are sent to the Corps, to avoid duplications of services.

"We don't try to be detectives, but we do feel we've been entrusted with the public's money and ought to spend it as carefully as we can," said Overton, of the Arlington Salvation Army.

Several private organizations also have sprung up to help the needy. Among them is AMEN (Arlingtonians Ministering to Emergency Needs), an all-volunteer organization that gets as much as $24,000 in county funds each year, to match private donations.

John W. Klein, AMEN's treasurer, said he hopes the county will continue to subsidize the program since the county subsidy in effect doubles the amount of money available. During the last fiscal year, AMEN spent nearly $35,000 to help 468 persons cope with emergency situations ranging from impending eviction and fuel cutoff to a need for food, temporary shelter or medical help.

Most requests to AMEN are for help in paying the rent, Klein said. The organization makes either interest-free loans or outright grants, he said.

Another group that helps needy people pay the rent is the United Community Ministries in Fairfax County. Director Eleanor Kennedy said such requests -- as well as requests for money to buy food or pay utility bills -- have increased to the point that the organization may need about 30 percent more money this year to meet the demands.

Last year, Kennedy said, the group helped about 9,400 persons. The budget this year is $190,000, but if current trends continue, she said, UCM might need $250,000 to keep pace.

"We're already beginning to feel the cutbacks in food stamps and medical services," Kennedy said. "And one thing that worries me is that people who live in trailer parks have already gone in to get their fuel assistance (allotments). You can only get that once a year, and it hasn't even been that cold, so I know we're going to be hit with requests for help on fuel.

"I hope the public response will be up," Kennedy added, echoing the prevailing sentiment, "because next year is going to be scary for all of us."