The fortress-like Soviet embassy here has become the nerve center for guerrilla operations against Rhodesia (Zimbabwe) and South West Africa (Namibia), undermining persistent Western hopes that Zambia's President Kenneth Kaunda would become the peacemaking moderate for southern Africa.

Behind the embassy's high, heavily guarded walls, a short walk from the Zambian foreign ministry, Ambassador Vasily Solodovnikov is intimately involved in training, supplying and even deploying guerrillas. Moreover, old diplomatic hands see him doing his best to scuttle Western efforts for negotiated settlements in Rhodesia and Namibia. For the Kremlin to cash in on its heavy investment, the guerrillas must win; a genuine free election might well install a non-guerrilla government.

The Soviet aim thus conflicts with popular sentiment in Zambia, possibly shared at heart by Kaunda himself, for a quick, negotiated peace in Rhodesia. Nevertheless, Kaunda publicly takes the hard line and may be trapped in positions not in his nation's best interest. Having mounted the Russian bear, Kaunda cannot easily get off.

Solodovnikov has impressive credentials. An expert at the Soviet Africa Institute with intimate links to the KGB, he was architect of the Kremlin's successful strategy for southern Africa. But the pudgy, smiling Russian is no KGB heavy, frightening off diplomatic colleagues. Rather, he assures everybody of his sincere best wishes for the Anglo-American initiative on Rhodesia.

Veteran diplomats don't believe a word of it. Solodovnikov supervised the quick buildup of Joshua Nkomo's new 3,000-man guerrilla army based in Zambia. Having put their money on this new military factor, the last thing the Russians want is a quick settlement.

Indeed, Solodovnikov has made Zambia a hub of military activity. It is a base for guerrilla raids against both Rhodesia and the long silver of South West Africa called the Caprivi strip-Aeroflot passenger planes land regularly at Lusaka, ferrying Nkomo's guerrillas to and from training in Angoloa.

But in typical Russian style, Solodovnikov is no gracious guest. While using Zambia as a base for military operations elsewhere, he is not beyong attempting a little subversion here. Some 250 Russian technicians, mainly teachers, are suspected by Zambian officials of proselytizing student radicals against Kaunda as an old fuddy-duddy with insufficient revolutionary fervor.

The matter surfaced when the Zambian government accused a Novosti press representative (undoubtedly a KGB man) of subversive activities and told Solodovnikov there would be no publicity if the agent were quietly returned home. The ambassador refused. The Zambian government then kicked out the Novosti man, announcing it in a brief item buried in Lusaka's government-controlled newspapers.

The Novosti incident is seized upon by Western diplomats as proof that Kaunda runs his own house, but it actually reveals Solodovnikov's arrogance and Kaunda's caution. Certainly, Kaunda is no free agent capable of throwing out the Russians in Egyptian-Sudanese fashion. Besides reliance on Soviet arms by the Zambian army (now deployed on the Rhodesian border), Kaunda is constrained by fellow "frontline" states (Mozambique, Angola, Tanzania) more radical than Zambia.

So, Kaunda's posture has hardened. The agent for Angola'a anti-Communist Unita guerrillas, backed by Kaunda in the Angolian civil war, has been thrown out of Lusaka. Although Kaunda once condemned Cuban intervention in Angola, he recently suggested Cuban troops might be used in Rhodesia.

Kaunda's switch from moderate to hawkish rhetoric on Rhodesia is attributed by Western apologists to disillusionment over past failures in negotiations. But beyond rhetoric, he single-handedly pushed the African summit meeting in Gabon to a resolution demanding military solution in Rhodesia. Western diplomats suspect a recent editorial in the Zambia Daily Mail, criticizing a suggested British Commonwealth peace-keeping force for Rhodesia, was written at the presidential palace. Above all, Kaunda is as committed to Nkomo's military force as are the Russians.

kaunda's militancy does not fit the national mood, which greeted war posters slapped all over Lusaka with ennui. Although depressed copper prices are mainly responsible for Zambia's economic hard times, closing the border with Rhodesia also hurt. Apart from student radicals, Zambians would rather spend money on Lusaka's wretched shantytown slums than for more Soviet military hardware. Even back-benchers in parliament are privately cool to the war effort.

Kaunda cannot change course to satisfy public opinion. He will ride the Russian bear until Soviet-backed guerrillas take over Rhodesia. Whether he dismounts at that point, nearly surrounded by leftist neighbors, is something Solodovnikov will have much to say about.