David Thornburgh, a senior at Haverford College, sent in an absentee ballot the other day for John Anderson, although he admits, "I suppose you could say it was a throwaway vote."

David, a political science major, doesn't think Anderson has a prayer of winning the presidency. He views his vote as a protest against the candidates the Republican and Democratic parties have dished up this fall.

He's tried to convince his father to join the protest. But his father refused to budge. His father is sticking with Ronald Regan, David says, because Reagan is "a candidate of the Republican Party, and he feels a certain obligation . . . that identification with a traditional party can be pretty strong."

David's father is Richard Thornburgh, the Republican governor of Pennsylvania, and one of Reagan's most influential backers in this pivotal state. He was no more successful in convincing his son to vote for Reagan than David was in convincing the governor to vote for Anderson.

But with the election only two weeks away and Anderson's standing in the polls plummeting, the question in this comfortable suburb on Philadelphia's Main Line and throughout the country is: how many of Anderson's supporters will stick with him until Election Day?

The word from the polls is not encouraging for the independent presidential candidate. The polls show that not only does Anderson have a far smaller percentage of the vote than Ronald Reagan and Jimmy Carter but that Anderson's supporters are less firmly committed to him and are slightly less likely to vote.

The word on the streets of Haverford is that an awful lot of people haven't made up their mind on how to vote. This is the kind of place where Anderson has always fared best. It is a predominantly white, affluent suburb with beautiful tree-shaded streets, large older homes and exclusive Haverford College.

Anderson has had an active campaign organization here since last winter with an energetic corps of volunteers led by Patti Gummere. His wife, Keke, visited here a couple of weeks ago.

Marjorie Johnstone has an Anderson bumper on her car. But when she was stopped on the street, she said, "I'm worried aobut Anderson being a spoiler. sWhat he'll do to this campaign bothers me. His lack of charisma bothers me. But I still like his willingness to say what he believes in regardless of the consequences. I've changed my mind twice. The other day my husband said, "Do you want me to take our Anderson sticker off? I told him, 'No, I'm still with him.'"

Anderson's supporters have been stereotyped as the "Chablis and Brie set" and "Volvo owners against the war crowd." Polls indicate they tend to be young, liberal, well educated, white and affluent.

"They're the better educated 25- to 40-year-olds, the upwardly mobile American voters," says Jane Fowler, Anderson's Pennsylvania coordinator. "They have good jobs. They like Chablis, Doonesbury and 'Saturday Night Live.' They are the good-government liberals. Not the old McCarthy or McGovern liberals, but the League of Women Voters liberals." m

"They are the uncomfortable voters," she continues. "They're uncomfortable with Reagan and uncomfortable with Carter. They really don't know a lot about Anderson. But they know they don't like the other two guys."

One American voter in 10 fits into the latter category, according to polls by The Washington Post. Anderson has the support of 36 percent of them. The same polls indicate that one-fourth of the people who voted for Sen. Edward M. Kennedy in the Democratic primaries now support Anderson.

Isabel Satterthwaite, a retired school-teacher and wife of an English professor at Haverford College, is one of them. It is late afternoon and she is seated on her tree-shaded patio waiting for cocktail hour.

"The question is why am I voting for Anderson when I could save the country from Ronald Reagan," she says. "My answer is that I don't see that much difference between them. I think Reagan is an incompetent, rather ignorant man. But I think Carter, whom I voted for four years ago, is almost as bad. He seems to get worse every day. He just hasn't been good for this country."

Satterwaite switched to Anderson after Kennedy's presidential bid failed, wavered for a while in September, and then settled on Anderson. Carter's campaign tactics played a part in her decision. "The personal insults he made on Reagan are simply awful," she says. "For this person who has portrayed himself as such a great Christian to do that is really hypocritical. It's almost Nixonian."

Polling data indicate Anderson has a very narrow, small political base. He has little support from blacks or the poor.

According to Post polls, he attracts 8 percent of the vote of persons who earn less than $8,000 a year, but 15 percent of those who earn more than $30,000. He attracts the support of only 6 percent of the people who finished their education with high school, but 18 percent of those who went to college. He attracts the support of 27 percent of the nation's student population, but only 9 percent of the people over 50 years old. He gets the support of 17 percent of the people who call themselves liberals, 13 percent of the moderates and 7 percent of the conservatives.

What the polls don't show is a sense of frustration among the educated elite that forms the core of Anderson's support, the feeling that the two major parties no longer speak to their needs, the sense that their lives and their futures aren't what they think they ought to be.

Anderson is their vehicle this election, and here is how two of them explain it:

Marc Zucker, a Haverford College senior: "I made a choice that I know wasn't a perfect choice. I'm impressed Anderson has adopted his positions along the way, that he has been willing to change. It would have been easier for him not to have to defend his positions on nuclear power and the Vietnam war for instance. But he admits his past mistakes . . . He is the only candidate who looks forward. He at least knows Americans are going to have to change the way they live. He has a real vision of where he wants a country to go."

Edith Jenks, 54, a lifelong Republican, and a school board member in the neighboring suburb of Radnor: "I call our generation the squeezed generation. I feel somehow we got left out. When I was in my 20s and 30s I thought that by the time I got to be 50 my generation, would be the one that called the tune. But I don't think we do.

"I have three daughters. They are all for Anderson. The things I've heard from Republicans and from Reagan are turning the clock back. I don't want my daughters and granddaughters to have the same problems I had as an ambitious woman. Anderson understands that and he is for the ERA. I've never bucked my party before but I feel very strongly that Anderson represents a much more middle-of-the-road candidacy than Reagan."