President Mobutu Sese Seko is riding high as he tours the mining-rich province of Shaba, which only a few weeks ago seemed fated to fall to insurgents based in Angola.

Although his regime is still dogged by problems that would have brought many government to grief, Mobutu has been receiving nothing but good news for the last few days.

Militarily, his troops, backed by 1,500 Moroccan soldiers, are slicing through western Shaba with the case the insurgents displayed in occupying it in early March. In neither case has there been much evidence of armed resistance.

Diplomatically, Nigerian Foreign Minister Joseph Garba confered with Mobutu in the Shaba provincial capital of Lubumbashi about mediating between Angola and Zaire.

Economically, the International Monetary fund announced yesterday that Zaire will receive $85 million to help stabilize its precarous balance of payments and cope with rampant inflation and copper prices that are still low.

In a telltale sign, several American construction workers are expected back in Kolwezi Sunday or Monday, it was announced.

Employees of the Morrison-Knudsen Co. of Boise, Idaho, they were part of a group of 77 American workers that withdrawn from Kolwezi in late March when the insurgents seemed about to take the copper-mining center.

The $500 million project they are working on involves constructing a high tension line for electric power from the Inga Falls near the Atlantic to the Shaba mining centers in eastern Zaire some 1,200 miles away.

The government justified the project by arguing it would make Shaba dependent on power from the rest of this sprawling country and help prevent the kind of secessionist tendencies that convulsed the mining province in the early 1960s and again over the past two months.

Mobutu was reported humiliated by the decision to pullout the construction workers, a step he took as a sign that the United States was abandoning him. Their return is bound to be interpreted locally as a sign of renewed American faith in the regime and proof it has weathered the storm.

Indeed, Mobutu was feeling jubilant enough to send a congratualtory telegram on the occasion of Tanzania's national day to president Julius Nyerere. The Tanzanian leader has not been on good terms with Mobutu, who accuses him of helping an armed opposition group on the western banks of Lake Tanganyika - and Tanzania's government-controlled press was one of the few black African voices to criticize the French airlift of Moroccan troops here earlier this month.

Yet, even as the Zaire-Moroccan force pushed west of Mutshtsha toward Diolo, a town on the Angolan border some 150 away, military observers are not sure Zaire is home free.

They believe it is too early to tell whether the insurgent force is going back to Angola or simply abandoning rail lines, roads and major towns the government and fanning out into the countryside to wage guerrilla warfare.

Mostly youhg recruits from Shaba's predominant Lunda tribe - with cadres supplied by Zaire army deserters and again veterans of the old Katanga secessinist gendarmes of the early 1960s - the insurgents are credited with guerrilla warfare capability.

[Havana, Radio, quoting "observers" in Lusaka, Zambia, attributed the Zaire-Moroccan advance to the Katangans shifting their tactics and "going into the jungles to proceed to guerrilla warfare," according to a broadcast monitored by the U.S. government.]

The answer may be supplied by the Nigerian mediation mission, which is designed to sort out bitter heritage of distrust bequethed by the Angolan civil war in which Mobutu and Angolan President Agostinho Neto were on opposing sides.

The Nigerians, who maintain good relations with both countries, have made it clear since they agreed to mediate in March that a battlefield decision was required before they could be effective.

The arrival of the Moroccans earlier this month was credited with having galvanized the previously sagging morale of the Zaire army. Indeed, reports from the field indicated the Zaire troops were so confident now that they claim the Moroccans are barely needed.

No one has said officially how long the Moroccans paln to stay. Obviously, their presence is a deterrent to the insurgents, who could well be waiting for their departure before rekindling the insurrection.

The timing of the IMF announcement appeared designed to bolster Mobutu and deter a consortium of private foreign banks from any temptation to cancell a $250 million loan.

Put together by the First National City Bank, the loan would be spread out over 1977 to help Zaire meet its heavy interest payment scheduled loans that were renegotiated last year.

Mobutu has yet to transform such outside help into the kind of solid political support that has been rule. The decline has been especially evident since a drastic drop in the world copper price in 1974 that left the country saddled with enormous debts.

Despite what the government-controlled press describes as his triumphal tour of Shaba, there, as elsewhere in the country, he no longer evokes great public sympathy. The steadily declining standard of living since independence in 1960 is of much more concern to the average person than battlefield victories.