Congress is moving to disassociate the United States from the government of Zaire, amid increasing alarm that President Mobutu Sese Seko may not be able to ride out a tide of growing discontent among his citizens.

Just before last week's summer recess, House and Senate conferees voted to reduce Zaire's foreign military sales credits from $10.5 million to $8 million, continuing what Rep. Stephen Solarz (D-N.Y.) termed "a process of incremental disassociation" from the Mobutu regime. The $8 million figure was reached after a move by some House members to uphold the previous House position and cut off all military assistance to Zaire.

"Our FMS (Foreign Military Sales) credits to Zaire provide a measure of identification with that government which we should try to minimize," Solarz said. "The Zairean government has completely lost the confidence of the people of the country."

The exact figure - $8 million or $10.5 million - is insignificant compared with the larger, more symbolic implication of the military aid reduction. The vote last Tuesday was, in effect, one of no confidence in Mobutu and his stated efforts to reform widespread corruption in his country and rebuild its army.

Since the May 1978 invasion of Zaire's Shaba province by Katangan rebels, when the Zairean army deteriorated into a mob of armed looters, French and Belgian military personnel have been trying to turn the Zairean army into an effective fighting force. The Zaireans soon will have to take over the security of the province from the predominantly Moroccan peacekeeping force uplifted there last year.

Lannon Walker, deputy assistant secretary of state, said he recently returned from Zaire and was "quite impressed" by the progress of its army since last year's Shaba debacle. The Carter administration had urged Congress too approve the $10.5 million in military credits, largely as a symbolic show of support for these reform efforts.

Also, the administration has been supportive of Mobutu because of the substantial economic and political stake this country has in Zaire.

Zaire is strategically located in the center of the African continent bordering Soviet-and Cuban-backed Angola. And Mobutu, for all the corruption surrounding him, has been a consistent protector of U.S. interests.

Also, Zaire currently owes $377 million to private U.S. banks and $300 million to various government agencies such as the Export-Import Bank. The Zairean government is bankrupt, and the only way creditors can hope for repayment is to encourage Mobutu's reform program while helping Zaire develop and economy based on mining cobalt.

Reform, observers agree, must begin with the army, which has been accused of plundering and pillaging. The peacekeeping force, which is scheduled to be withdrawn by Aug. 30, largely has been protecting the Zaireans from their army.

"The Zairean army is nothing more nor less than a rapacious rabble more intent on plundering the citizens' than protecting them, Solarz said. "They make the Kuomintang of Chiang Kai-shek look like an effective fighting force by comparison." Later, Solarz added, "Trying to reform the Zairean army is like trying to sell chastity belts to a whorehouse."

The conference report also makes it incumbent on the administration to receive "assurances" that the money will not be pilfered by corrupt Zairean officials as has happened with some other U.S. economic aid. But Solarz said, "As sure as you're sitting there I can assure you the administration is going to conclude there's been reform. Whether that's true or not is another question."

Walker of the State Department said the $8 million in military assistance will be only enough to allow the Zaireans to buy parts for, and make repairs on, equipment they already own. "Basically they voted for just slightly over a holding pattern," he said.

Walker said the Zaireans will "look to this as an indication of how serious we take the reform effort."