A United States flag waving from a government building is an unexpected sight in the Nicaraguan capital. But the Stars and Stripes have been fluttering in full view here at the main Nicaraguan government guesthouse where Jesse Jackson is staying during his brief Managua visit.
The ruling Sandinistas, beset by rising pressures at home, are treating Jesse Jackson as a friend - a friend who, they hope, will present their case to US liberals and minority groups.
Many Nicaraguans don't know quite what to make of Jackson. But they do know that ''that black man who wants to be president'' (as one Managuan calls him) may help them drum up opposition in the US to any possible invasion plans or other new, hard-line policies that the Reagan administration might choose to adopt.
Such hard-line policy choices, Nicaraguans fear, might well be adopted by Washington if the talks between President Reagan's special envoy to Central America, Harry Shlaudeman, and Nicaraguan Vice-Minister for Foreign Relations Victor Hugo Tinoco Fonseca fail. The talks are currently recessed after two opening days Monday and Tuesday in Manzanillo, Mexico.
Jackson comes at the time when the Sandinistas are beset by ever-increasing economic, political, and military pressures. It is a time of uncertainty, when almost any sign of outside support seems reassuring.
Yet, if reports now reaching Managua are true, the Nicaraguans are not about to be bailed out of their difficulties by the Soviets.
Nicaraguan junta leader Daniel Ortega Saavedra is now in Eastern Europe after finishing a visit with Soviet leaders in Moscow. According to one Western diplomat, Mr. Ortega went to Moscow for two reasons: to get massive Soviet assistance, which the Nicaraguans felt was necessary for their economic survival; and to negotiate the purchase of sophisticated military aircraft.
According to this and other Western diplomats, Nicaragua received little, if any, Soviet financial assistance. Nothing is yet known about the purchase of aircraft.
According to these diplomats and to a senior Latin American statesman, the Soviets do not want to subsidize ''another Cuba'' in Nicaragua. Nor are they willing to get involved in a military confrontation with the US in Central America.
The main problems facing the Sandinistas are the country's economic disarray and their own slippage in popularity among ordinary Nicaraguans. Both of these problems are partially linked to the military pressures on Nicaragua of the US-backed rebel contras.
Western diplomats and Sandinista officials say the economic disarray can be blamed on several factors: the economic results of US military pressure, Sandinista mismanagement of the public sector, and a private sector that refuses to invest for fear of confiscation of property and assets.
Linked to these are massive trade deficits and a severe shortage of dollars. The lack of dollars means that Nicaragua is afflicted by serious shortages of spare parts, fertilizers, and other products vital to the proper functioning of the country's largely agricultural economy.
More directly affecting the Sandinistas' political popularity are the shortages in basic consumer goods and foodstuffs and the price rises of many of these articles.
Many basic imported goods (toothpaste, for example) used by the middle classes and better-off segments of the urban working classes are either impossible to find or impossibly expensive. More important, there are shortages of the basic foods consumed by the majority of the population, including the two mainstays of the Nicaraguan popular diet, corn and beans.
In July, the Sandinistas plan to make two important changes in economic policy:
1. They will nationalize the distribution of six basic goods, including oil, sugar, rice, salt, and soap. From now on these products will no longer be bought at the market but only at government distribution centers. The aim is to cut out the profits charged by middlemen and to avoid hoarding and speculation.
2. They will reduce the massive subsidies on eight basic products, including corn and beans. The subsidies have been keeping those products' prices artificially low. In 1983 the subsidies accounted for 50 percent of all government spending, thus provoking massive, inflationary government deficits. The subsidies also discouraged production, since many peasants found it cheaper to buy beans on the market than to produce them.
According to one Western diplomat, these two measures will produce a ''little political time bomb'' for the Sandinistas. While shortages, especially of corn and beans will probably continue, prices will rise from 70 to 140 percent on basic products, says this diplomat.
At the same time, by nationalizing distribution of basic products, the Sandinistas will be alienating the market women and other Nicaraguans who have sold these goods until now. There are 35,000 such people in Managua alone - an important segment of the Nicaraguan masses to whom the Sandinista government has always looked for support.
Another measure arousing popular discontent is the military draft. Some 15, 000 men already have been drafted and another 15,000 now are being recruited.
It is impossible to measure popular support for the Sandinistas with precision. According to Western diplomats and other observers, one-third of the population clearly supports the Sandinistas while another third clearly opposes them. As for the remaining one-third, there are signs that discontent is growing among those who have been sympathetic to the revolution but critical of many Sandinista policies.
''People are beginning to lose hope that their life will improve under the (Sandinistas),'' comments one Western diplomat here.