Seated in a spare office in a converted row house across from Tom's Grill on H Street NE, a few doors down from a crowded employment office, Lawrence Williams pondered an upcoming deposition and a pretrial hearing on one of his 100 cases. He massaged his temples, pursed his lips. This one was different from the routine welfare and landlord-tenant cases he normally deals with -- he was about to go up against some of the best lawyers in town representing one of the city's most powerful banks.

His client, a welfare mother from Northeast Washington, had come to him in tears with an intriguing story of fraud and deception. And although his April schedule had been the most brutal in his 10 years as a lawyer with Neighborhood Legal Services, this was one he didn't want to blow.

The case probably will be heard next month in U.S. District Court. Williams' client had opened a checking account with a bank and had been given a 24-hour card, Williams recalled. One evening, she went to do some bank business and discovered that the bank card had her named misspelled. The woman said she went to a bank officer and turned in the card to him. She said the bank officer gave her a form to fill out for a new card and threw the old card in the trash can.

A few days later, the woman said, she learned that $790 had been withdrawn from her account. She said she didn't do it. When she asked the bank for the money, the bank said no way.

This is what Williams calls a general civil litigation case, the kind that makes up the bulk of the cases that his office gets. It is typical of cases brought in by the "new poor," people who have fallen off the ladder of middle-class life into the pool of poverty.

Williams' tenacious approach to the case makes it clear why some of the lawyers he has come up against would like to see the Reagan administration succeed in doing away with Neighborhood Legal Services. He has won more than 80 percent of his cases either through badgering -- he calls it negotiation -- or verdict. To him, legal services is a calling. With a background in civil rights, he figures the best way to help poor people is to be a legal advocate for them, offer professional help in addressing grievances.

One of his most storied cases is a lawsuit he brought against the District four years ago, challenging its water-billing system. A client had been billed $900 during a one-month period when other months prior to that showed only moderate water usage. Williams dug up evidence of an underground leak and claimed the city was liable.

Then he attacked the city's water termination statute, claiming water should not be turned off without a hearing. He lost in Superior Court, but appealed. Last month, he lost again before a three-judge panel of the D.C. Court of Appeals. But he appealed again to the entire nine-member court. The man just will not quit.

Meanwhile, his client still has water -- and the $900.

Williams estimates that a lawyer in private practice would have charged $5,000 to $8,000 to handle the water bill case over the four-year period. For his client the work was free.

Juggling his 100 cases through continuances and trial and tribulation alike is more than a full-time job for Williams. In April, he spent 15 of the first 20 days in court, jogging from Landlord and Tenant Court to Family Court to District Court to administrative hearings to judge's conferences. He is smooth-talking, confident and, at 38, managing attorney for the largest of the city's five Neighborhood Legal Services offices.

Williams' office has a staff of five lawyers, two of them on loan from Covington & Burling, which regularly contributes the services of its junior lawyers on a pro bono publico (for the public good) basis.

Williams grew up in West Virginia and graduated from high school in 1962. The son of a pipe fitter for Dupont, he worked his way through Howard University, with time off for Marine service, and then attended George Mason University law school. He became managing attorney of the H Street office last year.

Despite his efforts and those of his associates, though, the Reagan administration-backed 25-percent cut in funds has taken its toll, he said. "Too many people are not getting any help at all," he complained. "We are booked up for this month and probably won't be able to take any new clients until early June."

According to William Cook, director of Neighborhood Legal Services, the budget cuts have forced lay-offs of 27 staff attorneys and paralegals and the closing of offices on 14th Street NW and Nannie Helen Burroughs Avenue NE. As a result about 15 to 20 of those who call for help are turned away each day, Cook said. Neighborhood Legal Services' caseload dropped from 10,000 in 1981 to 7,000 last year.

Cook estimated that only about 1 percent of nearly 200,000 city residents eligible are receiving help. Eligibility is related to income -- clients who are single cannot earn more than $72 a week, though families are permitted to earn slightly more, up to $132 weekly for a family of four, for example.

The H Street Neighborhood Legal Services office refers most of those it cannot serve to Legal Aid, which is funded by United Way and the District of Columbia Bar Association and is the city's only other major source of free legal assistance in civil matters.

"We're busy, but we're not closed for intake yet," said Bill Perkins, managing attorney for the family branch of Legal Aid. The branch is in "a tight financial situation" and also has reduced its staff.

Meanwhile, the poor will just have to rely on the legal workhorses -- like Williams.

"The fact is most of the people who call us have bona fide legal problems," Williams says. "There are some whose problems would be better served by a social worker, but the great number of them are emergency legal situations."

About 30 percent of the cases are termination of welfare, 30 percent threatened evictions and the remaining 40 percent "general civil litigation," he said.

"The majority of the cases require immediate attention," Williams said. "We're like a legal aid ambulance. And the fact is, our efforts have stopped a lot of wrongful action against poor people by the government and big business. There are a lot of people out there with hair-raising problems, and we are the only place they can go to have their grievances heard."