Mozambique's warming relations with the West may be chilled by the latest raid into that country by South African forces. In particular, diplomats here see the strike by Pretoria against an alleged headquarters of the African National Congress (ANC) as ''embarrassing'' to the United States and a setback to its policy of ''constructive engagement.'' That policy has aimed at producing regional stability in southern Africa, partly through greater dialogue between Washington and Pretoria, which Washington hoped in turn would foster greater dialogue between South Africa and its black neighbors.
But the latest strike suggests:
* Tension between white-ruled South Africa and Marxist-leaning Mozambique may be on the rise again. Pretoria's campaign, using words and bullets, to force Mozambique to abandon all support for the ANC has not succeeded.
* Pretoria can penetrate virtually at will Mozambique's defenses, and could probably topple the government if it wished, say close observers here.
The South African Defense Force announced that a small task group had carried out a successful ''preemptive'' strike against the ANC Monday. The target was a building in the same neighborhood as the headquarters of the Mozambique defense forces and the home of President Samora Machel, according to the South African military.
Such a penetration must surely rattle the Mozambique government and its main benefactor, the Soviet Union. Mozambique was without a leader at home at the time of the attack, as President Machel was on a European tour regarded by many as an attempt by the former guerrilla leader to forge new links with the West.
Although South Africa termed the raid a success, the victory maybe bittersweet.
Despite four major cross-border raids by the South African Defense Force into neighboring states since early 1981, ANC acts of sabotage continue with regularity. Tom Lodge of the University of the Witwatersrand, an expert on the ANC, says flatly ''government reprisals don't seem to be effective.'' By his tabulation, there have been some 26 acts of ANC sabotage in South Africa so far this year, roughly on par with the number of incidents in 1982. And perhaps more important than numbers, the incidents continue to show greater sophistication by the saboteurs, Professor Lodge says.
In his assessment, the reason the sabotage campaign continues is that there ''are enough people and equipment in the country to continue at the present low level for some time.'' He adds: ''The ANC has reached the stage where (its operatives) can survive in South Africa for months at a time.''
President Machel's European tour follows warming relations between Mozambique and the US. Relations plummeted in 1981 after Mozambique expelled four US diplomats accused of spying. The US has just appointed a new ambassador to Maputo, the first since the 1981 expulsions.
The West seeks to reduce Soviet influence with Mozambique. And Machel's trip to Europe was seen as an attempt to encourage new Western investment in the country, ravaged by drought and increasingly challenged by its own guerrilla movement.
The Pretoria raid is ''distinctly unhelpful'' to both objectives, says Michael Spicer of the South African Institute of International Affairs. Mozambique's vulnerability to intervention is not apt to entice new investors, or to encourage Maputo to feel it can afford more independence from the Soviet Union, he points out.
The attacks throw cold water on hopes that Mozambique and South Africa were forging a more harmonious relationship. This is Pretoria's third major strike in Mozambique since 1981. And South Africa Monday threatened to mount more attacks on the ANC in Mozambique.
The 1981 raid set the precedent for South Africa's more aggressive regional policy of attacking what it regards as ANC targets in other countries. The most devastating raid took place last December, when South African commandos hit targets in Maseru, the capital of Lesotho, claiming 42 lives.
In one sense, South Africa's cross-border policy is bearing fruit. It has effectively intimidated most of its black neighbors from supporting what Pretoria regards as ANC operatives, although in most cases the host countries claim the targets are merely political refugees from South Africa.
The major exception in the eyes of Pretoria is Mozambique.
South African Defense Minister Magnus Malan said in a statement: ''Mozambique has been especially warned to get rid of the ANC. This government nevertheless is not prepared to heed these warnings.''
Mr. Malan charged that the Mozambique government helps the ANC with the planning of ''terrorist'' attacks, and harbors and provides ''facilities'' for the guerrillas. Maputo denies these charges.
Pretoria claimed its attack was preemptive, to foil a planned ''series of further attacks'' similar to one Oct. 10 in the small town of Warmbaths, near Pretoria. Petrol tanks and tankers were destroyed, but most alarming to South Africa was that the attack came one day ahead of a visit to the town by Prime Minister Pieter W. Botha.
Mozambique radio claimed the attack on alleged ANC offices resulted in at least five people being hospitalized.