For about a month now, Americans have been anguishing over the starving millions in Ethiopia, clogging the mails and telephone lines of relief agencies with an unprecedented flood of funds and volunteer labor. The famine, however, was documented to government and relief agencies two years ago.

The turning point was television. On Oct. 23, "NBC Nightly News" aired a British Broadcasting Corp. film of emaciated children huddled by the hundreds in squalid camps. The picture was horrible, riveting as only the sight of a starving child can be. The dam of apathy broke at both government and private levels.

The record of the U.S. response to word that 7 million Africans might die for lack of food is a lesson in the relatively feeble power of anything but television to galvanize the U.S. public -- and, thereby, to overcome political squabbling in the U.S. government.

Before Oct. 23, public and private U.S. food aid to Africa had been growing, but slowly. The major newspapers had run long articles on the growing disaster. Relief agencies had sent out mass mailings, churches pleaded for donations and funds were trickling in.

In Washington, bureaucrats and politicians had been arguing among themselves about the fact that helping Ethiopia meant helping a communist country, one whose chief denounced the United States almost daily. Decisions had been made to aid the people anyway, but the move was far from universally applauded.

In Ethiopia, secessionist rebels in areas worst hit by the famine had charged that the government of Lt. Gen. Mengistu Haile Mariam stole much of what relief there was and that the rest was mismanaged and did not get to the hungry.

Mengistu had spent an estimated $100 million in September to celebrate the 10th anniversary of the revolution that brought his army to power, and only after the celebration did he seem to focus on the famine.

For all these reasons, U.S. food aid to Ethiopia in all of fiscal 1984 was 41,000 tons, valued at $23 million. Mengistu called it a pittance, and it was, even though it was more than any other nation had provided.

In the two months since fiscal 1985 began Oct. 1, five times that amount has been committed. Of the 215,000 tons of food, worth $98 million, already sent or on the way, two-thirds of it was committed after Oct. 23.

More, much more, is in the works.

A mass mailing on Africa's agony from the Catholic Relief Services last March generated less than $800,000 nationwide. The phones started ringing Oct. 24, and more than $2 million has been donated since, according to director Lawrence Pezzullo.

"The media were just an incredible force in this," he said.

At other agencies, it is the same. "It wasn't just the United States that was slow; it was the world," said Carol Capps, associate director for development policy at the Lutheran Council in the U.S.A. "Now people are calling, doctors are offering services everywhere."

Aid authorizations now have committed the stock and funds available under Public Law 480, which provides free or low-cost food aid, and the Reagan administration will request more as soon as Congress reconvenes. After two years on the back burner, famine is hot politics.

The U.N. Food and Agriculture Organization spelled out the dimensions of the crisis in a November 1982 report, about the same time the Ethiopian government made an international appeal for help.

To many, reports of the spreading famine were just word of another depressing Third World problem.

"We would hold press conferences; we'd have a little bit of turnout but it wasn't widely reported," said Dick Loudis, assistant director of the Washington office of CARE. An ad hoc coalition of 15 to 20 private voluntary organizations began in the fall of 1983 to push for action, and they saw some movement.

"There were people at AID the U.S. Agency for International Development that just flat didn't want to do anything," said the head of a major relief agency who asked not to be named. "To them it was a chance to make communism look bad, that's all."

AID Administrator M. Peter McPherson denied that at the time, the official said, but investigated and found it to be true. He then took over the internal effort himself and was largely responsible for much of last year's progress, the official said.

Rep. Harold E. Wolpe (D-Mich.), chairman of the House Foreign Relations subcommittee on Africa, took a seven-member delegation to view Ethiopia's agony in July 1983, after The Washington Post ran a five-part series on the famine. "We were awestruck by the enormity of it," he said. A letter urging the Reagan administration to act was signed by 70 members of Congress.

Sen. John C. Danforth (R-Mo.) visited Africa in January and showed the resulting photographs to President Reagan. He expressed his shock to McPherson, who recommended that aid be sent to Mozambique, which also had a leftist government.

"That was a major break," said Loudis. "Reagan got into it and media interest picked up."

But television had not yet covered the story, in part because Ethiopia would not grant visas for camera crews.

"It was kind of a low priority with us," said Joseph Angotti, NBC's European news director, in a telephone interview from London.

In mid-1984 the Reagan administration decided to attach its effort to fund rebels in Nicaragua to a measure providing $150 million in food aid for Africa. After months of lobbying and promotional work by more than 60 relief groups, the emergency food aid had become a motherhood bill.

"Here was the administration saying okay on food if you give us guns," said Alex Rondos, director of the Center for Development Policy's Commission on U.S.-African Relations, a private educational organization. "What shocked me was the press: Clearly that was editorial material, but it wasn't, and that tells you something."

The issues were separated, and the food aid passed Congress.

In mid-October, a BBC crew led by South Africa correspondent Michael Buerk got into Ethiopia. Since the U.S. networks had withdrawn their Africa correspondents, the two six-minute films by cameraman Mohammed Amin of VisNews were the only ones around.

Angotti said he turned down the BBC's invitation to view the film before it was first broadcast. Then, he said, he saw it on the London news "and it just knocked us all right through the roof."

But NBC New York refused the story. Other NBC employes said New York was preoccupied with the U.S. elections and bored with the thought of another African famine. But NBC London sent the piece the next day "and it had the same effect there as it had here," Angotti said. The film ran that night.

"That was it," said Wolpe. "The facts were there for anyone who wanted to see them two years ago. To say that we were taken by surprise is only to say that we didn't want to see before."