THE SENATE Foreign Relations Committee is scheduled to hold a hearing Tuesday that almost everybody -- including most of its own members -- will ignore. As a result, a very likeable but thoroughly unqualified California businessman will almost certainly be confirmed as the new American ambassador to the southern African nation of Botswana.

Theodore C. Maino, the 69-year-old president of the Maino Construction Company of San Luis Obispo, is as solid a citizen as there could be. His curriculum vitae lists wartime service in the Naval Reserve, six years on the local school board and a stint as foreman of a county grand jury back in 1961-62. It also reveals that Maino is a member of the Boy Scouts of America, Rotary International and, most important in this context, the Mzuri Safari Club and Mzuri Safari Foundation. Mzuri is the Swahili word for "good" or "nice."

America's newest would-be diplomat is a big-game hunter. All last spring he shopped for an enbassy on the continent he so likes to visit. He tried, and nearly managed, to become ambassador to the large, strategic country of Kenya; but someone thought bettter of it and assigned him to a place where he could have almost as good a time but where his lack of diplomatic experience would be much less noticeable.

If Maino knows little about the turbulent politics of the region where he will serve, at least he is familiar with the animals. That puts him one small step ahead of Robert H. Phinny, 61, President Reagan's unfortunate choice as ambassador to Swaziland, also in southern Africa. At his own ever so brief confimation hearing last July 15 (attended and conducted by a single senator, Republican Nancy Kassebaum of Kansas), Phinny seemed utterly bewildered about the ancient kingdom to which he was being assigned. He misstated administration policy on at least one important point, implying support for South Africa's controversial attempt to transfer to Swazi control 2,000 square miles of land and the black people who live on it.

It is hard to understand why Phinny was appointed to a post in Africa, but it is easy to figure out how he got an ambassadorship in the first place. He is not just any decent, rich Republican, but the husband of the former Sally Gerber, of the baby food family. The list of his mother-in-law's donations to Republicans during the years 1978-1982 runs to 31/2 pages and includes many gifts to the Reagan campaign in 1980. Phinny gave $1,000 in 1980, and again in 1981, to something called the Gerald R. Ford New Leadership Committtee. The office address of his business, which manages the Gerber family's investments, is in Fremont, Mich., but he lists his legal residence and home address as Palm Springs, Calif.

In Maino's case, it is not so much a matter of large contributions as long affiliations with Republican candidates and conservative causes. He is a friend and occasional golfing partner of people close to the president.

Every administration in recent memory has named some ambassadors on the basis of political, rather than substantitive, considerations. Indeed, one of America's most famous and accomplished diplomats, David K. E. Bruce, was originally a political appointee. Mike Mansfield, the former Senate majority leader sent to Japan by President Carter and kept there by President Reagan, has served well, as has Arthur Burns, the former chairman of the Federal Reserve Board now serving in West Germany.

Political ambassadors of that caliber often do an even better job than career Foreign Service officers, some of whom lose touch with the American domestic political and economic issues that can be so important in foreign policy. Other career ambassadors are notorious sufferers from "clientitis," a tendency to overidentifty with the foreign country in which they are serving.

So it is not the number of Reagan's political ambassadors that is cause for concern -- at 30 percent, they represent about the proportion as under his predecessors -- but their quality, their judgment and their placement. John Louis, Reagan's envoy to the Court of St. James's in London, apparently was away from his post during the first 10 days of the Falkland Islands crisis and made no effort to hurry back. But even that is not so grievous an oversight in a large embassy with plenty of backup; it is in the smaller ones that ineptitude may have the greatest impact.

Africa seems to have been singled out as a particular ground for this administration's political appointees. Those with prior experience on the continent have performed capably -- including Herman Nickel, the former journalist who is ambassador to South Africa, and David Miller, a former businessman assigned to Tanzania. But appointments like this of Phinny and Maino (and their counterpart in Lesotho, Keith Brown, who was previously active in Colorado Republican politics) are impossible to justify. In each case, they replaced career diplomats with substantial African experience and special qualifications for their jobs.

The "BLS countries", as they are known (Botwana, Lesotho, and Zwasiland), are among the worst places for the United States to make mistakes today, given their location and their potential significance in the multiple crises besetting the region. King Sobhuza II of Swaziland recently died after ruling for half a century, and his successor, yet to be chosen, will have to make important decisions about relations with South Africa.

Lesotho, which is entirely surrounded by white-ruled South Africa, has often been been accused of harboring guerrillas of the African National Congress, and its own government is under siege from an increasingly violent opposition (which it believes is surrpetitiously aideddby the South Africans).

Botswana has fewer than a million inhatants, but it borders on South Africa, Namibia, Zimbabwe and Zambia; Angola lies just on the other side of a finger of Namibian territory called the Caprivi Strip. Thus geography dictates that Botswana have a role implementing any internationaly acceptable solutuion to the crisis in Nambia. Botswana also has a relatively healthy democratic system of government that the United States has been eager to help preserve. Whats more, as Maino will learn, perhaps with disappointment, it is a leader in African efforts to preserve wild game and control hunting.

The inexperienced political nominees to these trouble spots and other African posts have all undergone intensive turtoring at Foggy Bottom, but,during a recent conference here of American ambassadors to Africa, they failed to impress. One of them seemed especially confused between the names of countries and the names of their leaders, and he also woke up from a nap in the midst of one session and blurted out, "What's the IMF?" (the International Monetary Fund, which is active in aiding African governments).

But no one seems willing or able to do anything about this embarrassment for the United States. The "certificates of competence" that the State Department files with the Senate for such nominees are generally phrased in terms that could be used to describe anyone not charged with a crime. And their confirmation hearings are studiously avoided by senators, Democrats and Republicans alike, who then approve the nominations with scarcely a murmur of protest.