The deputy commander of the Zimbabwean Army was arrested today in connection with large arms caches discovered last month on farms owned by the minority political party of Joshua Nkomo.

Prime Minister Robert Mugabe fired Nkomo last month from the Cabinet, effectively ending the government coalition, and charged that he had plotted to overthrow the government.

The arrest today of Lt. Gen. Lookout Masuku, who commanded Nkomo's forces during the guerrilla war that led to independence, could lead to tensions in the 60,000-man Army in which Mugabe's and Nkomo's rival former guerrillas have been integrated.

So far, however, the announcement of Masuku's arrest seems to have been taken calmly, as was Nkomo's firing three weeks ago.

Top officers from Nkomo's former Zimbabwe People's Revolutionary Army who are now in the national Army "took it quietly," a senior officer at a military barracks here said.

The officer said Masuku had expected to be arrested ever since Mugabe indicated in announcing Nkomo's firing that some former officers of Nkomo's guerrilla army might be detained.

Arrested along with him were Dumiso Dabengwa, the former deputy commander of Nkomo's forces and now a civilian, and Swazini Ndlovu, a former intelligence officer in the forces who is now the chief political official of a black township near Bulawayo, Nkomo's tribal stronghold in southwestern Zimbabwe.

Masuku's arrest means that only one of Nkomo's senior guerrilla leaders remains a general. He is Maj. Gen. Javan Maseko, head of the quartermaster section.

More than 75 percent of 3,000 white officers have left the military since independence. A number of those remaining have praised Masuku and have generally preferred Nkomo's former troops, many with Soviet training, to soldiers from Mugabe's Zimbabwe African National Liberation Army.

Asked about the arrest, a white officer said, "I can't become embroiled in African politics."

Mugabe said that the arms discovered so far are enough to equip a brigade of 5,000. Nkomo has denied knowledge of the caches and said that both sides had stashed weapons all over the country for insurance. Mugabe has said Nkomo will be tried, although he has not been arrested.

There has been only one known incident of violence in the aftermath of Nkomo's firing. Thirty-two persons were arrested Monday night in the central city of Que Que after fighting between supporters of Mugabe and Nkomo.

About a dozen whites, including a member of Parliament, are being detained under emergency regulations on suspicion of plotting. Four whites went on trial Monday in Bulawayo charged with planning terrorism and sabotage in order to set up a republic in Nkomo's Matabeleland stronghold.

The trial promises unusual moments, since the prosecution says it has evidence that Bertrand, a candidate for Parliament in 1980, claimed to have obtained the blessing of an African spirit medium, Princess Violet Khumalo, to induce former Nkomo guerrillas to rebel against the government.