Rhodesian ground and air forces have launched their biggest raid into Zambia and fighting with the Zambian army was reported still under way late yesterday afternoon, more than 30 hours after the attack began.

The Zambian government said the "unprovoked and indiscriminate" Rhodesian attack involved the use of jets, helicopters and ground troops. It said the Zambian army has shot down six Rhodesian warplanes and that "gallant Zambian troops are containing the situation."

Zambia's communique said the attack came near the point where Zambia and Rhodesia meet Mozambique, which also came under Rhodesian attack recently.

Rhodesia, confirming the attack on Zambia, said it was aimed at preempting a major black nationalist guerrilla assault. It said 38 guerrillas were killed and a large quantity of Soviet arms captured or destroyed, with only one Rhodesian soldier killed. Rhodesia made no mention of any aircraft loss.

Western sources here said it appeared that the Rhodesian white-minority government intended to intimidate the two African frontline states into ceasing their support for the nationalist guerrillas now infiltrating into Rhodesia at a spiraling rate.

Both the duration and apparent magnitude of the Rhodesian raid appeared to mark a sharp escalation in the war and in its spread into all the neighboring countries. There were fears here that more such attacks on this country were likely in the coming weeks.

Precisely why Rhodesian Prime Minister Ian Smith chose this moment for an attack in Zambia was not immediately clear. But it seemed certain to court the condemnation of the U.N. Security Council and to tarnish the rhodesian diplomatic campaign to gain Western recognition of the internal accord on a formula for turnover of power to the black majority.

The brief Zambian communique made no mention of the involvement of the nationalist guerrillas in the fighting, and the Soviet and Cubanbacked Zimbabwe African people's Union (ZAPU), headquartered here in Lusaka, denied at first that its forces were taking part.

Nonetheless, it was widely believed here that the main object of the Rhodesian raid was to hit ZAPU's forward staging camps along the Zambian border to prevent a buildup of its forces there and their infiltration into Rhodesia.

In a similar air and ground attack into central Mozambique in late November, the Rhodesian security forces claimed to have killed 1,200 guerrillas belonging to the Zimbabwean African National Union (ZANU), the other wing of the guerrilla alliance known as the patriotic Front, ZANU said most of those killed were women and children.

The Rhodesian raid came as debate got under way in the U.N. Security Council over the whole Rhodesian issue and specifically the internal agreement sogned Friday between Smith and the three moderate, locally based black leaders.

There was no Zambian indication of the number of casualties sustained.

Contrary to the Zambian version, Rhodesia said all its troops had already returned to their bases. It named the main object of the attack as a guerrilla camp 10 miles west of Luwangwe. Zambia said the attack centered on that town, about 125 miles east of Lusaka.

There were unconfirmed reports that the Rhodesians had simultaneously hit several other camps inside Bishop Abel Muzorewa, leader of the Zambia.

In Salisbury, a spokesman for United African National Council and one of the black leaders who signed the internal agreement on Friday, said the bishop had not been informed ahead of time about the attack. "If he had been informed, he would not have been in favor of going ahed . . . we have arrived at this settlement to make peace and you don't make peace by crossing foreign borders," the spokesman said.

However, the other two black signatories, the Rev. Noabaningi Sithole and Chief Jeremiah Chirau, seemed more approving. Enemies of the agreement, said Sithole, will be opposed "with every bit of our lives.

The attack into Zambia has come only eight days after another Rhodesian incursian on into neighboring Botswana in which 15 Bostwana soldiers and two civilians were reported killed.

At the United Nations, African members of the Security Council are expected to call upon the world body to reject the internal Salisbury agreement and to support the external Patriotic Front, whihc has been largely responsible for Smith's decision to accept black majority rule by the end of this year.

The internal agreement establishes a multiracial interim government led by an executive council on which Smiht, who remains as prime minister, is to sit together with the three black leaders.

The five frontline African states supporting the Patriotic Front have condemened the agreement out of hand and vowed to continue supporting the Front's Liberation struggle.

Zambia is one of the foremost proponents of the nationalist war and main backer of the ZAPU wing of the Front.In a television interview Friday, Zambian President Kenneth Kaunda pledged to continue his backing of the Front.

"What choice have we? . . . We will not forfeit them like the West has done," he said.

ZAPU, which is led by Joshua Nkomo, has been repidly building a large guerrilla and professional army with the help of the Soviets, who are providing the arms, and the Cubans, who along with the East Germans, are partly responsible for their training in camps here and in Angola.

It now has perhaps 6,000 trained guerrillas ready to join the struggle inside Rhodesia, and this new force is known to be causing considerable concern in Salisbur.

In an interview Feb. 17, Nkomo said that his ZAPU guerrillas were intent upon hitting the white Rhodesian government hard now to "finish it up" and that he expected Rhodesia to hit back in a struggle to the end.

To date, Rhodesia has largely spared Zambia from the kind of pounding it has directed against guerrilla camps in Mozambique. However, a harbinger of the changing Rhodesian policy toward Zambia came Feb. 7 when Rhodesian helicopters and airborne commandos were used in a brief strike on a ZAPU camp across Lake Kariba in Zambia.

Although the Zambian government denied that the attack too place, Western diplomatic and other unofficial Zambian sources reported that around 50 ZAPU guerrillas were killed.