Instead of air-conditioned hotel rooms, they sleep in tents and hunt shade where they can during the 100-degree-plus days. Instead of coming by plane, they came by van, car, and Greyhound and chartered bus.
But then no one invited demonstrators to the Republican National Convention.
Few in number compared with the demonstrators outside the Democratic National Convention in San Francisco last month, they nevertheless represent such a wide variety of causes that their leaders had to struggle to thrash out a ''platform'' on which the groups could agree. That platform calls for full employment, a better environment, an end to discrimination on the basis of sexual preference, class, or race, a reversal of the arms race, open borders, and passage of the ERA, among other things.
''What we have in common is to see that Ronald Reagan is removed from office, '' says Leslie Cagan, one of the leaders. She was busy setting up a press conference by the groups under one of the open-sided tents set up here on a bank of the Trinity River, within a mile of the Convention Center.
Her own group, Mobilization for Survival, opposes nuclear energy and nuclear weapons. One of the largest groups represented, the Association of Community Organizations for Reform Now (ACORN), is critical of President Reagan's cuts in social programs for the poor.
Others here oppose a US military presence in Central America. Linda Nye, who earns her living selling roses for commercial florists, is one of those. Like many who came here to protest, she does not have the answers, only a deeply felt sense that something is wrong.
''People are being murdered and tortured'' in El Salvador, she said quietly at a rally of some 1,500 demonstrators here Saturday night. She wore the yellow ''One world/one planet'' T-shirt of the ''peacekeepers,'' some 125 demonstrators who took several hours training in nonviolent methods of crowd control.
Near the back of the crowd at the rally site - the memorial to President John F. Kennedy, who was assassinated here in 1963 - sat Brad Allen, an engineering student at the University of Houston. This was his first protest, he said, though his parents often publicly protested the Vietnam war.
When asked why he was here, he replied, ''I got scared,'' noting that several replacements on the US Supreme Court were likely to be made during the next four years. He says he does not want Mr. Reagan to be the one to make those appointments.
The crowd ranged from retirement age to young parents with babies and included blacks, whites, Hispanics, and others. Most wore jeans or shorts; a few dressed in eccentric costumes.
''I'm kind of awed,'' said one young man who was not a demonstrator and said he had come to see the crowd. Paul Geilich, a Dallas lawyer, who visited the tent city of the demonstrators here, said, ''I am diametrically opposed to the majority of causes represented here.''
As noted by banners held aloft in the march from the tent city to the rally site, the first of several protest events this week, the groups represented included: Palestinians; homosexuals; socialists; communists, in addition to ACORN members.
Charles Spaberg, a San Fransisco credit-union employee, wearing a T-shirt marked ''GAY,'' said he would like to see better legal protection for homosexuals from job discrimination. ''I've lost dozens of jobs,'' he said, claiming he was forced to leave when employers learned he is homosexual.
On ACORN's side of the tent city, Perla Cardenas, sits on the ground, under the shade of a tent, with her two children: one 5 years old, the other, 15 months. ''The economy is supposedly getting better, but it's not getting better for the friends I know mostly.'' Currently unemployed, she lives on $148 a month in Aid to Families with Dependent Children and another $199 in food stamps.
Fred Kirkwood, a former Mississippi sharecropper now retired from factory work, rode a bus here from Chicago. Holding his straw hat in his hands, he recalls the Great Depression of the '30s and says: ''I'm scared Reagan is going to put us back in the same shape.'' His $556-a-month social security supports him and two other people. ''I need help,'' he says. ''I ask the Lord every day to give me wisdom and knowledge.''
Dallas city officials initially resisted some of the plans of the demonstrators. But a court order and an apparent desire on the part of city officials to avoid bad publicity has so far resulted in close cooperation between demonstrators and police and other authorities. The city even provided the tent city site with sanitary facilities, water, and access roads.
A chain-link security fence that encircles the Convention Center, and the location of an approved demonstration site on one side of the center, however, make it likely that most delegates will not see the protests this week.