President Kenneth Kanunda, who has ruled this country since it gained independence 14 years ago, faces a serious challenge in next week's presidential election.

Elections in black Africa seldom return incumbent presidents with less than 90 percent of the vote. Thus it is something of a tribute to Zambla's election process that practically no one expects Kaunda, 54, to do better than squeak through the country's fourth presidential election next Tuesday. He is running for another five-year term.

In the last election in 1973, the Zambian president was returned by 85 percent of the vote. But the downward turn in his popularity and the general Zambian disenchantment with the then new, single-party system was clearly reflected in the low turnout -- less than 40 percent of registered voters.

This year, there are predictions that less than one-third of the 1.5 million enrolled voters may go to the polls and that Kaunda may get the necessary 51 percent of the vote by only a small margin.

The question being pondered by concerned Western embassies, which naturally favor Kaunda, the most pro-Western of the African "Front-line" leaders involved in the Rhodesian dispute, is what happens then.

Perhaps Kunda will go on ruling as before; But a minority president in black Africa, where military cups are all too common, psses concern.

Under the Zambian constitution, if Kaunda fails to be reelected he would stay on for three months as a care-taker president while the party holds another congress to select a new presidential candidate and organize a second election.

Kaunda has no official opponent. He is running against himself and the problems of a bankrupt, copper-based economy with long lines outside shops for even basic necessities like butter, flour, salt and the staple corn.

In fact, a candidate could not dream of worse circumstances in which to run for reelection. Not only is Zambia flat on its back economically, but it is caught up in an unpopular war and taking a beating from Rhodesian air and ground attacks on suspected guerrilla bases.

Kaunda would seem to have every reason to call for a postponement of the elections due to the national crisis. But he promised last year they would be held on scheduled and he has kept his word.

The reelection of a president, Zambian style, involves a curious mixture of Western campaign techniques and authoritarian African tactics.

The state-controlled press has been singing the praises of Kaunda for weeks now and castigating what appears to be a strong bid by opposition elements, many within the ruling party, to turn out a large "no" vote.

The United National Independence Party, the country's only legal political body, has hired a British campaign consultant to oversee a high-powered publicity campaign to sell the president to a weary and unhappy nation. The campaign includes bumper and wall stickers that say "I Will Vote for KK Dec. 12" and show voters how to put a cross next to the party emblem, an eagle with its wings stretched in a "V" shape.

The hare, the symbol for "no" votes is conspicuously absent. (An initial attempt by the party to have a snake for "no" votes was ruled unfair).

An American soul singer, Sal Davis, has written a special song dedicated to Kaunda, "Son of Africa, Loved by Everybody." It plays on the raido and television along with plugs for the president.

The first party slogan for the election was "KK -- No Change," but Kaunda's opponents soon twisted it to "KK -- No Chance." Also, his supporters realized that a promise of no change at a time when the country is wallowing in economic problems and under Rhodesian attack was perhaps the wrong approach and the slogan was quietly dropped.

Another slogan seems more appropriate to selling the president: "KK Is the Man for Unity." Party officials stress at rallies around the country that Kaunda has successfully maintained the "fragile union" of Zambia's 73 tribes. They urged voters to return him as the best insurance against tribalism and disunity.

While campaign techniques may be Western-influenmced, the calculated elimination of all opposition candidates and the careful "votting," or disqualifying, of even longtime party officials running for the National Assembly seems more African in style.

Changes in the party's constitution this fall disqualified two well-known political figures, Simon Kapwepwe and Harry Nkumbula, from the presidential race. Kapwepwe was at one time Zambia's vice president and Nkumbula was a founder of the nationalist movement against British colonial rule.

Both failed to meet the altered qualifications for entering the presidential election and the party unanimously endorsed Kaunda as its sole candidate to the post of party and state president in early September.

Elections for the 125 seats in the National Assembly have not been noticeably more democratic. Even after local ruling party officials carefully scrutinized contenders for the October primary election, the party's Central Committee decided that 30 of those who won were unworthy candidates and barred them. Only two were reinstated.

One of those who won but was struck from the list was Arthur Wina, a former minister of finance and education and for the past five years an outspoken National Assembly deputy from Livingstone.

During the primary elections, in which only party members participate, Wina got 270 votes and his closest rival only 64. "The next thing I heard was a newspaper report that I have been betted," Wina said in an interview at his farm outside Lusaka.

To this day, he has not been officially told why he was disqualified.

His elimination is thought to be tied to the party's drive to stifle opposition in the National Assemby. Wina is a persistent and embarrassing critic of Zambian socialism and a vocal proponent of restoring capitalism.

While sharply critical of the party for becoming "rigid and ideological" Vina believes that the forthcoming election will be honest and accurately reflect whether Zambians approve of this new authoritarian trend as well as Kaunda's leadership.