Congress has approved spending $500,000 to train Afghan rebels in public relations techniques in a bid to win the propaganda war over the Soviet occupation of Afghanistan.

The training is likely to include sending Afghans into the war zone with video cameras to tape the fighting and alleged Soviet atrocities and sell it to the American television news networks.

The approval of funds came in the dying days of Congress last week when Sen. Gordon J. Humphrey (R-N.H.) successfully proposed an amendment providing an additional $500,000 to the budget of the United States Information Agency (USIA).

Humphrey, who accused the Reagan administration last December of "serious mismanagement" of U.S. aid to anti-Soviet guerrillas in Afghanistan, has pushed through Congress other measures to boost the propaganda war against the Russians.

These include authorizing the establishment of a "Radio Free Afghanistan" under the auspices of the Board for International Broadcasting which oversees and funds Radio Liberty. The idea would be to broadcast directly to the Afghan people in their own languages, similar to Radio Free Europe's longstanding transmissions to Communist countries.

A second measure includes showing three USIA films about Afghanistan inside the United States, possibly on college campuses. Normally, the USIA is not allowed to distribute or show its films in America, but Humphrey has secured a congressional exemption in this case.

Yesterday, the USIA said it was too early to explain how it intended to spend the $500,000 extra funds for training Afghans. "We are looking at the matter right now and will be ready to say something by October 1," said a spokesman.

According to the amendment, the funds will be used to "promote the development of an independent media service by the Afghan people and to provide for the training of Afghans in media and media-related fields."

Humphrey offered some suggestions last June when he spoke on the Senate floor, after securing approval for the funding from his colleagues during private meetings with staff and other members.

"As a practical matter, it will involve the training of Afghan journalists and providing them with mini-cameras to take video footage of the war as a means of getting out the message to the world on what is going on there,"he said.

One of Humphrey's aides said yesterday that the film footage could be sold to the American television networks.

Though major American newspapers and most of the television networks have sent reporters into Afghanistan to cover the war, some critics argue that it has been neglected as a major news story.

Rosanne Klass, director of the New York-based Afghanistan Information Center, said she has been in contact with Humphrey trying to obtain funding for two Afghan news sources based in Peshawar, Pakistan.

Yesterday, Mohammed Salehi, from Itehad E-Islami, the new alliance of seven Afghan political parties, said of the action, "Of course we are pleased because there is very little about the Afghan story in the media," he said. "But, remember, this is not the same as antitank missiles, which we also need desperately."