Is UN chief walking into a trap, or opportunity, in Namibia?

Namibia, an issue as thorny as the prickly pear tree that inhabits the arid regions of southern Africa, vies with the Middle East as one of the United Nation's most enduring perennial problems.

Thus, as UN Secretary-General Javier Perez de Cuellar heads to southern Africa this week, he has no illusions that he can get Cuban troops out of Angola or have South Africa remove its military presense from Namibia and Angola.

If he could achieve these goals simultaneously, the Namibian problem - which has been before the UN virtually since its inception - would be resolved. But that right now seems a remote, if not impossible, scenario to many UN officials. So many question the wisdom of the Secretary-General going to southern Africa and running the risk of returning home empty-handed.

That Mr. Perez de Cuellar decided to go at all - a decision taken only after much deliberation - was because he felt he should leave no stone unturned in the quest to nudge the territory toward independence.

While the Secretary-General's visit will provide at least the appearance of momentum on the deadlocked issue, some UN officials wonder if he may be walking into a trap.

Their reasoning goes something like this: The Secretary-General would have to visit both the South African and Namibian capitals in order to demonstrate his impartiality. (South Africa has frequently questioned the UN's impartiality on the Namibian issue.)

He also may be obliged to meet with about 40 minor political parties. This would upset the South West Africa People's Organization, which sees itself as the sole legitimate representative of the Namibian people.

Some UN officials see no hope of advancement in such a tangle of meetings and divided interests, and many think Namibia is no further from independence than it was 5, 10, or 37 years ago, when South Africa began it illegal occupation of Namibia.

That skeptical view is not shared by at least two members of the ''contact group'' - the group of Western nations that came together five years ago to try to work out settlement on Namibian independence.

The two members, Britain and the United States, say there has been considerable advancement in the settlement process. They say there has been progress on such issues as the kind of election to be held in Namibia, the role of peacekeeping forces in the region, and simultaneous withdrawal of South African and Cuban troops.

The reason for the gulf in perceptions between the West and the third world on how far or how close a Namibian settlement is depends largely on how the parties read South African intentions.

To the West, South Africa appears to have made concessions, leaving only one key obstacle: South Africa's apparent overriding preoccupation with Cuban troops in Angola.

While the Reagan administration says the US does not insist on removal of Cuban troops as a precondition, the issue deserves consideration because South Africa sees the troops as a legitimate security concern.

To critics of the Pretoria government, the question of Cuban troop withdrawals is an extraneous subject that was never an element of UN Resolution 435, the 1978 statement which all parties have agreed is the basis for Namibian independence. Such critics say they have become so wary of delays on negotiations that they suspect South Africa is stringing participants along in order to buy time.

Those close to the southern AfriGan situation think that right now South Africa is under no real pressure to compromise.

This is because the country is strong: The front-line African states that border South Africa are against the ropes economically. And South Africa's allies in Angola, Jonas Savimbi and his rebel National Union for the Total Independence of Angola, are reportedly scoring major military gains and keeping Angolan government troops at bay.

Until South Africa finds it is in its best interests to negotiate, few at the UN see much prospect for a solution on Namibia.