When Shehu Shagari narrowly won the presidency four years ago, he was by his own account the "reluctant" candidate, put forward because there was no taint of financial corruption on his record.

Last month, Shagari, 58, won his second and, by law, final presidential term with an unprecedented mandate. His National Party swept the subsequent elections for the two legislative houses by such margins that Shagari felt the need to assure Nigerians their country is not headed for one-party rule.

The contrasts between 1979 and today are stark. The president then was hesitant, constrained by the need to form a coalition Cabinet after winning only a third of the vote in the five-man presidential race. This time, with 48 percent of the vote in a field of six and no need of a coalition, an element of steel has become apparent in his post-electoral style--particularly his warnings against fresh outbreak of the political violence that plagued the August voting.

Less than a week after the victory, Shagari announced at a press conference that all ministers, government agency chairmen and advisers were to submit their resignations by Sept. 30 "so that I can set up a new government." In putting together a new administration, he said, "one has to reexamine the structure with a view to improving it."

In his first four years, Shagari was persistently characterized by critics and supporters as honest, fair, humble and peace-loving. He is widely considered to be respectful of the judiciary and a supporter of civil rights.

A Moslem, Shagari warmly welcomed Pope John Paul II during his February 1982 visit.

For all Shagari's vaunted honesty, critics charge that he has been surrounded by powerful, corrupt politicians who have enriched themselves with government funds while operating in the president's name. Shagari has said that while there is corruption in Nigeria, it is not as deep nor as widespread as his detractors would make it.

Chinua Achebe, a prominent writer and a political opponent of Shagari, has responded: "Shagari is neither a fool nor a crook, so I must assume he lives abroad."

Shagari "should return home, read the papers and from time to time talk to Nigerians outside the circle of presidential aides and party faithfuls," Achebe wrote. "Corruption in Nigeria has passed the alarming and entered the fatal stage, and Nigeria will die if we keep pretending that she is only slightly indisposed." He then listed some examples.

On the issue of political violence, Shagari spoke out recently at the launching of election rounds that had to be postponed in August in the states of Ondo and Oyo because of such fighting.

Shagari warned the politicians who "incite their supporters to acts of violence" will be prosecuted with the full backing of his administration. "Any Nigerian who, in spite of these admonitions, deliberately takes the law into his hands by inciting the public to violence, encourages the use of libelous and provocative utterances or engages in subversive acts for that matter, will definitely not escape the wrath of justice," he said.

In the same speech, Shagari tried to put aside fears that his party's overwhelming victory could lead to a one-party state.

"The fusing together of the very diverse groups in Nigeria into one political party is totally impracticable and, in the Nigerian situation, can never work," he said. "A thorough study of the history of this country and its political development will confirm that the only avenue to popular leadership is a strongly based democratic system which would allow for free and fair competition for political offices amongst many political parties," he added.

In his own indirect way, Shagari is letting Nigerians know that things will be different the second time around.