The fate of 450 detainees being held at Nsawam prison 15 miles north of here is becoming a major political issue between the military government and the Ghana Bar Association, which is leading the civilian opposition to it.

Gen. I. K. Acheampong, head of the ruling Supreme Military Council, insists there are no "political detainees" anywhere in the country and that the inmates of Nsawam, a medium security prison, are all "criminal detainees." But the bar association asserts that they are all political detainees and that there are many other such prisoners in jails elsewhere in Ghana.

The question of human rights and civil liberties has become a burning one as Ghana approaches the March 30 referendum on whether the nation is to return to civilian party politics or accept a joint military-civilian "union government."

Opponents of Acheampong's proposal for such a government complaint that they are having a great deal of trouble arguing their case and that the largely state-controlled media are heavily slanted against them. In addition, they are upset by the rough tactics being used by the military government's supporters to silence them, apparently with impunity.

One meeting of professional people here Oct. 12 was reportedly broken up by thugs who invaded the Accra community center while police stood by and took no action to stop them.

Acheampong strongly condemned the incident and has speadedly said that his government will uphold the right of dissenters to speak out freely against the union government plan. But his opponents remain skeptical, saying a large number of persons have been imprisoned for their political views.

The bar association has set up a human rights committee to defend these detainees and on Dec. 13 obtained a writ of habeas corpus from the Accra high court for the release of 175 of the Nsawam prisoners.

The military government had only let 19 of them go before it decided to ignore the court order and even rearrested those who had been released. Thus the fate of all the Nsawam prisoners remains in doubt.

The bar association maintaining that the 175 Ghanaians covered by the writ were taken into custody without any court order or executive decree. Some have been in jail since shortly after Acheampong led a coup in January 1972 against the last civilian government under K. A. Busia.

"The bitterest complaint we have had from them is that they were just rounded up and not told what they had done wrong," said association president W. N. Aduma-Bossman at a press conference earlier this month.

Asked at this own news conference two days later about the possibility of a general amnesty for all political prisoners. Acheampong replied that his government's desire for a national reconciliation of Ghanaians of all persuasions did not mean support for "anarchy."

After first stating that each case would be judged on its individualments, he quickly added "there are no political detainees, this I can assure you . . . Either they have been convicted and jailed for offenses, or whatever, but there are no political detainees."

He said the government had received a number of petitions asking that certain "hardened criminals" be put behind bars to protect the public and that it had in fact put many away.

Whether the 450 Nsawam prison inmates are "political" or "criminal" detainess, Ghana is scarcely what one would call "police state" under Acheampong's largely benevolent rule. Even bar association president Aduma- Bossman admits that "there has been considerable progress in understanding the right to dissent since the end of the second republic." He was referring to the Busia government.

It also appears that there are relatively few lawyers, doctors, teachers or students among those who have been taken into custody, though it is these groups who are the sharpest critics of the Acheampong government. Aduma-Bossman named one or two professionals and described the vast majority of the Nsawam prisoners as "people in very ordinary situations, like shopkeepers."

A visitor to Ghana today cannot help but be struck by the way in which many Ghanaians opposed to the union government proposal criticize both it and military rule in public places as well as their homes. No one seems terribly concerned about being arrested by plainclothes policemen lurking in the shadows.

As the state of human rights goes in African countries these days, Ghana could hardly be described as a serious offender. So far as this reporter could ascertain, not one Ghanaian, civilian or military, has been executed despite at least three unsuccessful attempts to overthrow Acheampong. Surprisingly few civilian politicians have been jailed recently, despite a nearly successful strike against the government last summer.

However, an undetermined number of students involved in anti-military demonstrations earlier this month were reportedly arrested here and in Kumasi. Some were released the following day, but not all of them.

The real problem for Acheampong's civilian opponents appears to be primarily the lack of opportunity to make their views known to the public. The country's two largest daily newspapers, and the national radio and television, are all state-controlled and give little time to airing opposition opinion.

Another legitimate concern of dissenters here seems to be the threat of intimidation and even bodily assault, by civilian supporters of the military government. No one seems to be interested, or able, to curb their excesses and none of the professionals at the community center has been arrested.

Meanwhile, the issue of whether there are really political detainees is still being fought out in the courts between the government and the bar association. The association has just cited the military authorities for contempt of high court in refusing to release the 175 Nsawam prisoners.