The Rhodesian government, in a promised crackdown, reportedly has rounded up more than 300 black nationalists officials associated with the two guerrilla factions fighting to overthrow the faltering biracial government.

A spokesman for guerrilla leader Joshua Nkomo's Zimbabwe African People's Union said that at least 320 officials of his group have been arrested and that the police were apparently seeking others. The government has not commented on the arrests.

The police also raided some of the party's offices and official's homes, seizing documents and other materials, the party spokesman said.

The arrests follow Prim Minister Ian Smith's declaration Sunday that the government planned "to liquidate the internal workings" of groups inside the country linked either to Nkomo's organization or Robert Mugabe's Zimbabwe African National Union. The two make up the Patriotric Front, the guerrilla alliance operating from Zambia and Mozambique.

Five members of the People's Movement, the pro-Mugabe organization here, are also known to have been arrested.

The crackdown on the internal opposition is one of several measures Smith promised to strengthen the government's hand in the escalating guerrilla war. The other main one is the imposition of martial law in some areas.

The arrests, in effect, are undoing one of the few actions of the transitional government since its creation in March. At the insistence of the ruling Executive Council's three black leaders, more than 800 political prisoners were freed last spring.

Now, it appears that as many as half or more of them are likely to be arrested again, complicating Western and African diplomatic efforts to bring both Patriotic Front and internal leaders to the negotiating table.

Nkomo has already declared that the all-party conference being promoted by Britain and the United States is "dead and buried." Observers here doubt this is his final word, however.

It is still not clear whether the government intends to ban the People's Movement and Nkomo's party outright, but the general assumption here was that it probably would not go that far.

"They haven't said anything about it yet," said the Nkomo spokesman. "They are just eliminating the leadership to cripple the organization. But it is too late. We will go even if they ban us."

Most of those arrested to date are district, provincial and national party officials and include 10 members of the 60-person National Executive Council, he said. But four top internal leaders, among them party vice president Josiah Chinamano, escaped arrest by leaving the country just beforehand or were already abroad. All four were reported to be in London.

The main thrust of the crackdown has been against Nkomo's organization, apparently because Nkomo took responsibility for shooting down an Air Rhodesia passenger plane 12 days ago and because the party has a far more extensive legal organiztion inside the country than the People's Movement.

The transitional government lifted the ban on Nkomo's group only last spring, but the one on Mugabe's faction was kept on to give a rival one, under the Rev. Ndabaningi Sithole, a member of the Executive Council, a chance to supplant it.