Few other places in this rangeland town of 9,000 were as brimming with good feelings last week as the classrooms of the local Head Start center. Thirty-five children, all from poor families, were enjoying the attentions of a staff that had recently celebrated -- with a community-wide party -- the 20th anniversary of the Head Start program.

Two thousand miles east in Washington, where the program began as part of Lyndon Johnson's "Great Society," politicians and some 250 Head Start friends were having their celebration. They met at the Hart Senate Office Building for a rooftop reception to recall the early days in 1965 and to remind the nation that Head Start, with a current budget of $1.07 billion, is the most successful and most visible federal child-development program.

In remote rural communities such as Rawlins, once a thriving cattle town but now raveled in economic depression, the necessity of the program is obvious. The services provided by Head Start -- education, nutrition, health care, parent involvement, referrals to social-service agencies -- are counted on by families or single parents who have little. Carbon County, of which Rawlins is the biggest town, is larger geographically than Connecticut. It is also immeasurably poorer. Mines -- coal and uranium -- have been closing.

Amtrak no longer serves the town. The local Catholic school is shut. With fewer jobs, population is declining.

The losses place all that much more pressure on the Head Start center. America is fast becoming a nation of poor children. Last week, the Congressional Research Service and Congressional Budget Office reported that 22 percent of the nation's children live in poverty. That is up from 13 percent in 1969. Worse, government spending for poor children dropped by $290 each from 1976 to 1983. No other age group is as poor as America's children.

In Rawlins, the director of the Carbon County Child Development Program, which serves 135 children including those in Head Start, is Al Kirsh. His overall budget is $250,000, which doesn't include the six-classroom building donated by St. Joseph's parish, the local Catholic church. Kirsh, on the scene for a number of years, is seasoned and knows that under the Reagan priorities the needs of poor children are being pushed further and further aside. He has praise for his staff and the families. When he walks the halls between the Head Start classes he knows the names of the children. He gives them a pat and a kind word.

He has other words, too: "I think the funding is atrocious for what the federal government wants the Head Start program to do." He tells of lacking money for something so basic as building maintenance: "Last winter on many days, there was a 20-degree difference in temperature in the west side and east side of our building. The wind comes from the west, but with poor insulation and poor caulking on the windows, the bitter cold comes in. If we had money, we could put in double-glazed windows. As it is now, the heat bills are enormous."

Few of the nation's 1,281 Head Start centers do not have a similar story of need. Nor is there one that couldn't enroll more children if money were available. The program currently cares for 452,250 children -- the enrollment since 1965 is 9.1 million -- but officials report that only one out of five of the eligible preschool children is being served.

Critics of poverty programs are currently trashing them as though the country never had worse blights or scams. Distinctions don't seem important, so many of the critics get away with their generalized blasts. If taken program by program -- Head Start, Legal Services, VISTA, Job Corps, Upward Bound, Foster Grandparents -- a modest success story has been unfolding. It is modest for the obvious reason: the programs, like Head Start, have been given the money to serve only a small percentage of the poor.

As if to eye every nickel, Head Start has been excessively monitored. Some 1,500 evaluation studies have been done since 1970. One conclusion has emerged: The benefits to children -- from gains in later schooling to few cases of anemia -- have been lasting.

No one needs proof in Rawlins. A staff worker calls the local center, in the simplest language, "a life-saver." She said that with the economy blowing out, merely providing breakfast and lunch for the children would justify the program.

In the playground behind the center the other morning, children merrily enjoyed their games and the warm prairie weather. This, too, was part of the Head Start celebration. "Critics of poverty programs are currently trashing them as though the country never had worse blights or scams."