The mood in Rhodesia is a bit like that in a darkened theater between acts ofa powerful dramatic performance. Some people are still sitting in stunned silence, some are struggling to comprehend what they have just seen, while others are waiting for the lights to go up and the discussion and criticism to begin. In a cliffhanging final act just before the curtain went down (at midnight, Jan. 4) on a British-sponsored cease-fire for the seven-year-old bush war here, thousands of Patriotic Fron guerrillas materalized out of the dense woodlands of Rhodesia. Now, fully 18,500 guerrilla fighters are said to be gathered at some 16 camps scattered across this southern African nation. The last-minute rush of armed fighters confounded many observers here. At midweek, halfway through the seven-day cease-fire period, even Patriotic Front co-leaders Joshua Nkomo and Robert Mugabe were predicting that the deadline for reporting to cease-fire camps might have to be extended. But the "bush telegraph" that has operated among the guerrillas so effectively during this country's seven years of battle got the word to the small cells of guerrillas operating in isolated areas of the country. They surged into the camps in unexpectedly large numbers. Predictably, the appearance of so many rifle-toting black youths -- their average age is surprisingly low -- has sparked a mix of acclaim and criticism. Some people here, especially whites, are openly skeptical. They note that front spokesmen earlier had claimed there were "substantially in excess of 31, 000" guerrillas fighting under the organization's banner. And they ask the whereabouts of the remaining 12,500 guerrillas who are not in the camps. The generally young age of the guerrillas who have turned up -- some are as young as eight -- has convinced others that the front is deliberately keeping its seasoned fighters out of the camps in case the cease-fire breaks down and the war breaks out again. According to this theory, inexperienced new recruits or "mujhibas" -- youthful lookouts -- are being armed and sent to the camps to "pad the numbers." But others see the massive turnout of guerrillas as proof of the front's readiness to end the war and to try to win electoral control of the country in the coming majority-rule elections, scheduled for late February. British government representatives here seem guardedly optimistic about the progress of the cease-fire. "The PF [Patriotic Front] have clearly made a serious effort to gather their forces," says spokesman Nicholas Fenn. Mr. Fenn also made two significant announcements: that South African troops are inside Rhodesia "with the Governor's agreement" to protect Beit Bridge, over the Limpopo River boundary between Rhodesia and South Africa, and that Rhodesian security forces have been deployed to assist police in dealing with continuing "lawlessness" in the country. Meanwhile, the battle for control of Zimbabwe, as Rhodesia will be called after it becomes independent from Britain's rule after the elections, already is moving from the battlefield to the sports field, as it were. A sports field in the Highfields suburb of Salisbury was the scene of a massive rally by Bishop Abel Muzorewa's United African National Council (UANC) on Jan. 6. It marked the official kickoff of the bishop's campaign, although his party has been campaigning for well over a month. The bishop (formerly Prime Minister) castigated his chief opponents before a crowd estimated at more than 50,000 people, charging that their Marxist leanings would plunge the country into chaos. Equally vituperative words had been sounded on the same field just a week previously, when the Mugabe Zimbabwe African National Union (ZANU) wing of the Patriotic Front held a rally. Most observers agreed the crowds drawn to each rally were roughly equal in size. But the ZANU crowd came mostly on foot, while Bishop Muzorewa's supporters were bused into Salisbury from across the country. That underscored the difference in the campaigns so far. The bishop's UANC is running a slick, well-financed, Western-Style campaign, complete with professionally produced flags, banners, placards, and buttons. The Patriotic Front rally was a less organized affair. Banners and posters were largely homemade, the campaign paraphernalia missing, the sound system defective.