Staring into space, Robert Lowe sits in a corner of a small rented trailer, two blocks from Interstate 8 in this dusty desert 10 miles from Mexico. At 58, he has a degenerative brain disease.

He worked as a cook once, his wife Mildred reminded him, but that was 1977 and he cannot remember that far back.

A few months ago the government wrote Lowe and, ignoring his failing memory and his regular dizzy spells, told him a doctor found he could walk steadily; his $397 monthly Social Security disability check would be cut off.

Lowe has begun a struggle to get the money back, but the federal agency set up in the Great Society to ease the plight of poor people -- the Legal Services Corp. -- can no longer do much for him.

At the California rural legal assistance office 25 miles from here in El Centro, where the federal program operates, the staff told the Lowes "they could help me only a bit of the way, their hands were tied," Mildred Lowe said.

The office has lost two lawyers and a secretary to federal cutbacks and new rules have restricted the kinds of cases they can handle, while the slumping economy and cuts in other programs like Social Security have brought a flood of new people asking for help.

Although fall is always bad for jobs in this farming community, this September the unemployment rate was 38.9 percent, compared to 30 percent in September, 1981.

"There are just too many clients, and not enough personnel," said Pedro Nunez, 33, a law clerk in the little office on a rundown block of El Centro.

The area is dotted with vacant lots where buildings had to be torn down because of a recent earthquake. The legal assistance staff must pare down their caseload just as ruthlessly, telling clients like the Lowes that they are going to have to handle their problems on their own, armed only with whatever advice the staff has time to give. Clients with a "marginal defense," a legal problem that would probably require lengthy appeals to solve, also are being told they must represent themselves.

To Jose Padilla, the 30-year-old directing attorney of the office, the handling of the Lowes is akin to feeding lambs to lions, particularly in cases where a tenant or consumer is going up against a landlord's or a store owner's attorney.

Padilla grew up in this flat, irrigated desert country, full of poor immigrants from Mexico. He said the local courts and hearing boards "still give them a chance to be heard, but when they are opposed by an attorney, that voice doesn't mean much."

Lupe Quintero, a 34-year-old community worker assigned to the office, said that welfare offices and other government bureaus that delay checks or cut off benefits "treat these people very badly" when they try to protest. Many of them are like Lowe, with serious physical or emotional problems, and with the added handicap of no longer being able to count on inexpensive legal assistance.

"When you have people who have mental cases, it worries you," she said, "because you don't know what they might do."

The state headquarters for California Rural Legal Assistance in San Francisco has cut staff at all its county offices, although program officials appear relieved that the system has so far survived threats from Washington to shut it down altogether.

The headquarters also has lost the lobbyists it once employed in Sacramento, San Francisco office executive director Alberto Saldamando said, making it more difficult to influence the state law dealing with the poor.

"I am good in my job and so is Lupe," said Steven L. Jones, 41, who has served 12 years as a community worker in the El Centro office. "We believe in what we are doing and that we take care in investigating a case. But we've got so many people in here that I can't do it. I went six years without losing a welfare hearing, then I lost one because I had too many clients."

Without the time to investigate fully, Jones went to a welfare hearing with only one independent affidavit testifying that a father had really abandoned his wife and three children. The woman had to survive six more weeks without her needed welfare payments, going deep into debt to friends and relatives, until Jones was able to get four more affidavits and a statement from the husband himself verifying the situation and winning restoration of the benefits.

Republican critics of government legal assistance for the poor have argued that private attorneys doing charity pro bono work could fill this gap. But lack of funds has forced the local bar association in El Centro to close its lawyer referral service, which offered initial legal advice for just $2 to poor clients whom the federal program could not handle.

Saldamando complained of a continued political assault on his activities. An absentee landlord in Los Angeles, he said, recently called to complain about a legal assistance suit against a property the man owned in Salinas. Saldamando said the man said he planned to call Washington and see if the matter could be solved by cutting off Saldamando's funds.

Padilla noted little such harassment in El Centro; to him the fund cutbacks and new rules on litigation to take effect in January are bad enough.

After Jan. 1, the El Centro office will not be able to help undocumented workers from Mexico. Proof of legal residency will be required before any new case is taken. To Quintero and Jones, this is blatant discrimination, one more way to keep the poor from their door.

"But if that's what we have to do to keep the door open," Jones said, "that's what we'll do."