About 65 people had gathered in the cafeteria of Fontana High School to ask Rep. George E. Brown Jr. (D-Calif.) some questions. At 62, entering his 10th campaign for the House, Brown has stuck his familiar round face, with cigar and glasses and rumpled hair, into every corner of his slightly redrawn 36th Congressional District.

He is in more political trouble than any other liberal Democratic congressman in southern California. Every major Republican fund-raising group appears to have him on its hit list.

But in this dry, flat little town at the southwest corner of San Bernadino County grow the seeds of another possible victory for Brown.

Fontana lives off a large Kaiser Steel plant, which is in serious trouble. From a peak of 8,500 workers in 1979, employment there is down to 3,900 and is scheduled to drop soon to 2,500.

The audience gathered from this traditional Democratic stronghold largely blamed the calamity on the Republican administration in Washington. Brown did what he could to encourage these working-class Democrats, who retain some admiration for President Reagan and some ambivalence about their own party, to at least send him back to Congress.

Alma Scott, 69, a Fontana housewife, spoke with a voice shaking with rage: "The people in Washington, why don't they cut their own wages? Why doesn't Reagan cut his? Why don't they cut Nixon off from all the money he is getting? And they are sending it overseas when they need it at our backdoor."

The questions were mostly friendly, with widespread applause greeting Brown at the end.

He has paid particular attention to senior citizens' groups because this area of southern California has become something of a Mecca for people looking for cheap land where they can park their mobile homes and enjoy a fairly inexpensive cost of living. He said 20 percent of the district may be senior citizens.

"A hell of a lot of those people are Republicans, but they are single-issue Republicans," he said. "Anyone who threatens the Social Security system is in serious trouble."

People in the district "basically still think that Reagan is a good guy, the guy with the white hat on the white horse. They can't believe that he is doing something that is hurting them."

Perhaps sensing the lingering respect for the president, Brown's criticism of Reagan in public was respectful and somewhat detached, although he indicated privately he was building up to tougher talk later in the campaign.

"You have to figure out for yourself how a conservative president can pile up the biggest deficit in United States history," he said in Fontana.

The president's efforts to raise the military budget and cut social programs "is not necessarily bad," Brown said, continuing his muted criticism. "I happen to disagree with it because I think it's running the country toward war. Those of you who agree with the president ought to go out and vote for him."

At all of the senior forums, Brown was asked about threats to Social Security. Among those at the North Norton Senior Center in San Bernadino were Leilla Darnall, 64, a retired railroad clerk, and Albert Speier Jr., 71, a retired production superintendent. Both said they would vote for Brown but still generally blamed the Democrats for the economic mess the country had fallen into.

Both bristled at the suggestion that cost-of-living increases in Social Security might be restricted. "We're not getting enough as it is," Speier said.