Rhodesias daring decision to launch a major air and military attack deep inside Mozambique last week has led to serious questioning here about what what motivated the attack and its wide publicity at one of the most delicate moments in Rhodesia's 11-year-old crisis.

During the seven-day punitive raid, it was billed here as the most serious setback to date for insurgent forces, a boast apparently designed in part to prove that Rhodesia was not succumbing to the pressures of the rapidly escalating, four-year-old war.

After Saturday's withdrawal, however, doubts about the reasons behind it remain, especially in light of the timing.

The strike came in the midst of the latest Western peace initiative, just a few hours before the four-member Anglo-American team left Salisbury for Maputo, the Mozambique capital. The Rhodesian action could jeopardize this last-ditch settlement effort by angering not only the black nationalist leaders but also the leaders of the black African states most involved in the conflict.

In addition, the Rhodesian's reluctance to provide details - after the initial unprecedented publicity - has added further mystery to the situation.

The know facts are few and comparatively unimpressive:

Thirty three guerrillas were killed, a small number in comparison with the hundreds who died in the two previously acknowledged raids into Mozambique. Nor were there any prisoners reported captured, again a change from previous strikes.

Two of the four insurgent bases hit were deserted when the Rhodesians arrived, indicating either poor Rhodesian intelligence or a leak to guerillas.

The quantity of captured arms shown journalists - who were not allowed near the border post from which the raid was launched - was meager: a few rifles, rocket-propelled grenades, a machine gun and a single antiaircraft gun - all of Soviet or Chinese manufacture. After a November 1976 raid, 80 tons of war materials were put on display.

MAPAL, 60 miles inside Mozambique, was billed as the main guerrilla center between the Rhodesian border and the Mozambiqu* e capital, and therefore an important target. According to a Portuguese who lived in Mapai more than 25 years, however, it barely qualifies as a village.

The element that makes the strike most curious is the fact that Rhodesia commandos are widely believed to have crossed the border more than 100 times on so-called hot pursuit operations. Mozambique puts the number of possibilities:

First, the two previously publicized raids coincided with important political turning points. The August 1976 strike on Nyadzonya camp, when more than 300 guerrillas were reportedly killed, was launched just as former U.S. Secretary of State Henry A. Kissinger began pushing for a settlement. The attack on six camps in both northern and southern Mozambique last November - when several hundred were said to have been killed - came in the middle of the Geneva peace talks between four black nationalist leaders and Prime Minister Ian Smith.

The Rhodesian government does not want to appear to be in a weak position during negotiations. Setting back the guerilla campaign and nationalist morale may push the African leaders into a peaceful settlement deal according to this argument. To achieve this the government may be willing to endure international condemnation.

Second, the raids are somewhat necessitated by the growing number of guerilla attacks. The hard-pressed Rhodesian forces cannot hope to shut off all the 1,704 miles of hostile border with Mozambique, Zambia and Botswana. Preemptive strikes are aimed at getting the insurgents before they can enter Rhodesia.

But for either reason, was the raid worth the heavy price tag, politically or militarily.

It is believed here that last weekend's shellings of Kariba on Rhodesia's nothern border with Zambia were in retaliation for the Mozambique raid.

This is the first sign that there may be some coordination on the two fronts, until now operating separately. That could be a debilitating blow to Rhodesia's counter-insurgency campaign.

Politically, the raid may have angered black nationalists - specifically Joshua Nkomo and Robert Mugabe, who have formed the militant, Soviet-backed patriotic front and who have the backing of guerillas in both Zambia and Mozambique - into balking at further negotiations via the Anglo-American team, or into hardening their terms.

Perhaps even more importantly, the five so-called frontline African countries - Mozambique, Botswana, Zambia, Tanzania and Angola may also refuse to back the Western settlement attempt.

Three of the five now have hostile borders with Rhodesia, all the scenes of clashes with Rhodesian forces within the past four weeks.

The raids on Mozambique have led to increasing speculation in Maputo that the government will call in outside help. It is doubtful the Mozambique will continue to tolerate such deep Rhodesian penetrations.

This would amount to a commitment that would probably end Mozambique interest in any settlement.

Many Western diplomats in Africa say that Rhodesia may be trying to get Mozambique to call on Cuba and the Soviet Union for help. The diplomats think that Rhodesia might feel that such an action would heighten its chances of getting assistance from South Africa and the United States.

The peace talks are now hanging by a thin string that could break at the lightest push. Smith is willing to extend the current property and educational requirements that now qualify about 6,000 blacks - out of a black population of 6 million - for the vote. He is not willing, however, to implement the principle of one-man, one vote, as demanded by the British and some of the nationalists.

The negotiations on terms cannot go on indefinitely. The Anglo-American team is reportedly aiming at a late autumn deadline. The slow pace of the talks, while the military tension increases, does not bode well for peace.

Although the Rhodesians may not have intended to sabotage the talks and their hopes for peace - in fact just the opposite - the impact of the Mozambique raid could, in the long term, do just that.

New agencies reported these other developments:

Guerrillas bombed a railway line used by Rhodesia to send goods to South Africa. A spokesman said the line was out of commission seven hours. There was no casualties, he said.

The Rev. Ndapaningi Sithole, a Rhodesian black nationalist leader who has lived in self-exile in Zambia to two years, said he intends to return to Rhodesia in the near future.