President Agha Mohammad Yahya Khan seldom ventures out in public without a swagger stick tucked under his arm, even when wearing a business suit.

Associates say he does it to preserve an image as military commander in chief with a caretaker role in public life. But time and the tides of Pakistani politics and civil strife have obscured the image of the man and the future of his country. When General Yahya replaced Mohammad Ayub Khan as President in March, 1969, one of his first orders of business was to pledge his determination to establish a civilian, democratic constitutional government, disclaiming any personal ambition to continue the autocratic rule of his predecessor.

Yesterday-two years, one month and 28 days later-the President, meeting foreign correspondents for the first time since the outbreak of fighting in East Pakistan two month ago, again declared that he was determined to bring about a civilian government.

It was clear, however, that he was finding the deed more difficult than the word.

President Yahya, pronounced YA-YA, now 54 years old, had been a military man all of his adult life until he assumed power two years ago. The descendant of a long line of military men, he attended military schools fought in World War II and in the 1965 war with India over Kashmir and rose rapidly through the ranks of the Pakistani Army.

YOUNGEST BRIGADIER

Known as "The Chief" to his men, he was, at 34, the youngest brigadier, at 40 his country's youngest general, and in June, 1966, at the age of 49, Pakistan's youngest commander in chief.

Since becoming President he has wrought some changes: curbing business monopolies bringing corruption charges against hundreds of former officials, raising minimum wages, increasing allocations for education and development, and fostering the election of a National Assembly last December- the first free national election In 23 years of Pakistani independence.

But in a nation of 130 million people, where more than 20 political parties compete for attention and where poverty is widespread, the very meaning of democracy and constitutional government Is a matter of dispute.

Although the President says he seeks eventual civilian rule, he has repeatedly demonstrated that military power is the nation's cohesive force, at least for the time being.

AN EXACTING SOLDIER

A stocky, silver-haired man with heavy eyebrows and a big chin, President Yahya is described by fellow Officers as an exacting professional soldier in public and a convivial conversationalist in private.

He was born in Peshawar, on the Northwest Frontier of British India, on Feb. 4 1917, into the historically important Quizil-bash family, whose name means "red turbans." The family was descended from the elite soldiery of Naga Shah, the Persian ruler who conquered Delhi early in the 18th century.

At 18 he entered the Indian Military Academy at Debra Dun and was graduated with the title of King's Cadet, awarded for being first in his class. He later attended Punjab University.

In World War II, he saw action in Egypt Libya and Italy, and when India was partitioned in 1947, he set up the Pakistani Staff College, having been promoted to lieutenant colonel.

As he rose quickly through the military ranks, he became closely associated with President Mohammed Ayub Khan and was reported by British sources to have been a key figure in the coup d'etat that brought General Ayub to power in 1968.

In the 1965 border war, General Yahya was awarded the Hilal-i-Jurat, Pakistan's second highest military honor, for his performance in the Chamb sector. The President is married, and has one son and one daughter. In keeping with Moslem custom, his family keeps discreetly in the background.