Cape Town — It was made dramatically clear recently to a group of South African politicians who visited Mozambique just how fragile that country's government control of its own territory is.
As the visitors' plane approached the international airport on the outskirts of the capital, Maputo, a voice on the intercom announced: ''The aircraft's lights will be turned off now for security reasons.''
Evidently, the rebel Mozambique National Resistance (MNR) movement was a menace just a few miles from Maputo center.
That was two months ago. More recent reports indicate the rebels have been curbed.
Mozambique has a form of defense treaty with the Soviets, but it was more practical for many reasons for President Samora Machel to turn for help to South Africa, his neighbor and by far the most powerful country in the region.
His most persuasive argument was a warning that unless help was forthcoming and violence was curbed in his country, a nonaggression treaty between South Africa and Mozambique would be in danger.
This treaty, signed last March and known as the Accord of Nkomati, has immediately benefited South Africa because it has eliminated Mozambique as a staging post for African National Congress insurgents.
But high expectations in Mozambique that the accord would bring peace and a flood of investments that would revitalize the economy have not been born out, something that has been exploited by Mozambicans opposed to any deal with ''racist South Africa.''
South Africa responded to President Machel's appeal by acting as broker between the rebel MNR and the Mozambique government, finally negotiating a form of cease-fire that was ratified in the South African administrative capital, Pretoria, at the end of last week.
Although South Africa formally welcomed the result of the Pretoria negotiations, South Africa's President P. W. Botha himself acknowleged that the outcome is far from certain and that ''the path that lies ahead will be rocky and fraught with danger.''
It is also likely to be confused by murky political connections and power play.
For a start, there is the question of South Africa's own relationship with the MNR rebels. For years it was alleged that South Africa was backing this organization as part of a ''destabilization'' policy aimed at ousting Marxist Machel and promoting a form of government in Mozambique that South Africa would find more acceptable.
South Africa has denied any connection with the MNR.
But just a day before the Pretoria agreement was reached, the Mozambique government put on display in Maputo about 140 MNR prisoners. Several of them said they had been trained at secret bases in South Africa.
Even if South Africa is sticking to the letter of the Nkomati Accord - as it has said repeatedly that it is - and denying any support to the MNR, there are suspicions that money is being sent to the rebels from Portuguese sources in South Africa.
There are are a considerable number of people in South Africa who fled from Mozambique 10 years ago when Machel and his Frelimo Party gained power.
Another threat to peace is that even if the MNR leaders agree to a binding cease-fire - and both MNR and the Mozambique government have denied that fighting will stop immediately, whatever happened in Pretoria - it is questionable whether they would be able to enforce their will on all the people who are fighting in the name of the MNR.
Many of these people are not motivated by any political ideals, but are just bandits living by violence.
In terms of last week's Pretoria agreement, South Africa has been asked to play a role in enforcing a cease-fire. Speculation that this might mean committing South African troops in Mozambique was reinforced at the weekend by South Africa's defense minister, Gen. Magnus Malan.
He said at a political congress that South Africa ''must remain prepared to act against terrorists even within some of our neighboring states.
''This holds true even if we should conclude defense accords with all our neighboring states, (which) may seek our assistance in helping to protect their sovereignty,'' General Malan continued. ''We are, and remain, a regional power bearing particular responsibility for regional security.''
If this should mean that South Africa will send troops to Mozambique, it could have various political implications.
For a start, it does not seem that it would be sufficient to send in a token force. It would require fairly considerable numbers to police such a large country effectively.
And the South African government could be embarrassed at home if it is accused of propping up a Marxist government.
However, South Africa may feel intervention is justified if meant a political compromise in Mozambique that would change the complexion of the Maputo government to something more acceptable to the West generally.
Also, although South Africa has denied direct support for the powerful Angolan rebels led by Dr. Jonas Savimbi, it has made no secret that it is very friendly toward him - even to the extent of making him welcome at the installation last month of P. W. Botha as state President.
If South Africa could act successfully as a peace broker in Mozambique, it might be encouraged in a similar process in Angola.