Secretary of State Cyrus R. Vance said yesterday that the "Katanga gendarmes" who have crossed from Angola into Zaire could pose "a dangerous situation" for that nation's stability if they threaten Zaire's copper mining belt.

Vance nearly doubled the original figure supplied by the Carter administration the day before on the value of the U.S. emergency airlift of military and medical supplies being sent to Zaire.

"The total amount of the cost of this equipment is less than $2 million," he told the House International Relations Committee, rather than $1 million. "That's all that we have said we will do at this point," Vance testified.

While most members of the committee, and of Congress as a whole, raised few questions about the administration's description of the new U.S. involvement in Zaire as "limited," Rep. Don Bonker (D-Wash.) expressed serious concern.

Late yesterday, after hearing a U.S. intelligence version of the fighting in Zaire's Shaba Province, formerly part of Katanga and the homeland of the troops who have entered Zaire, Bonker said: "I think this could potentially be as big as Angola, in a different way."

What is developing in Zaire raises "substantial issues which President Carter will have to face," said Bonker.

Bonker, who helped to forde a congressional cutoff of Central Intelligence Agency financing of support for pro-Western factions in Angola's civil war in 1975-76, questioned Zaire President Mobutu's ability to counter any serious military challenge. "His army is fairly corrupt and ineffective," said Bonker, although Zaire is receiving "half of all our military assistance to Africa."

Vance told the committee in other portions of his testimony that:

The presence of Palestinian Liberation Organization representatives at a United Nations reception for President Carter in New York Thursday night does not mean the United States has changed its policy of refusing to recognize the PLO. The White House issued similar disclaimers, although israeli Ambassador Simcha Dinitz officially expressed his country's "strong feeling and concern" about the U.N. invitation.

The United States and Cuba are now "in direct contact" on negotiations that could lead toward normal relations. Most previous negotiations have been handled through the Swiss, but Vance said direct talks are now possible on a U.S.-Cuban fishing zone, renegotiation of an antihijacking accord that expires in April, and other issues.

Although Zaire has charged that the military forces crossing its border are led by Cubans in Angola, Vance said "we have no hard evidence" that Cubans are participating in the incursion. Upwards of 10,000 Cuban troops are still estimated to be in Angola, after spearheading the pro-Maxist victory in Angola's civol war.

The Katangan units reported to be intering Zaire are portions of an estimated 6,000 troops, including families, who supported the unsuccessful attempt of Moise Tshombe in the 1960s to establish a separate Katangan nation in Zaire's cooper mining region. The Katangese troops. along with the Cubans and others, later fought on the side of the anti-Western faction that gained victory in Angola.

Zaire puts the number of Katangans and others who have crossed its border in recent days at 5,000. One U.S. intelligence estmate puts the figureat 2,000. According to sources in Belgium, which formerly ruled Zaire as the Belgian Congo, the figure is 500 to 800.

Vance, using no figures yesterday, said, "The force appears to be made up primarily of katanga gendarmes, as they are called . . . They have been engaged in conflict in the southern area of Zaire . . . along the routes to the copper mines.

"If something happens to the copper mines," Vance said, "it would be a very severe blow to the government of Zaire." He said, "As to what the future holds, no one can tell at this point."

Vance said that the first load of U.S. supplies sent to Zaire on Tuesday was about 35,000 tons of equipment, and "the next load which will complet the shipment" will include spare parts for C-130 transport planes, redios, batteries, rations and helmets.

The administration, he reiterated, already has authorization for the military supplies for Zaire, out fo $30.2 million authorized for this year. When asked by Chairman Clement Zablocki (D-Wis.) about possible use of Americans in "a peace-keeping force" for Zaire. Vance said, "No such thing is under contemplation at this point."

Rep. Dante B. Fascell (D-Fla.) asked whether internal forces in Zaire might join up with the border-crossers, and Vance said, "One hears rumors of that from time to time."

In Brussels, the clandestine Zairese opposition party, the African People's Party, called President Mobutu "a cynical dictator." This party said it is an ally of the Congolese Liberation Front, which last week claimed responsibility for the invasion of Shaba Province.

On the PLO dispute, Vance treated it as a minor matter. He said U.N. Secretary General Kurt Waldheim "asked us whether we wished to indicate who should be invited" tot he reception for President Carter Thursday night. Vance said, "We indicated to the Secretary General this was a U.N. function," and that was up to the United Nations.

White House press secretary Jody Powell made a similar comment yesterday and said there was "absolutely no political significance" to the PLO inclusion on the list of invitees.

Israeli Ambassador Dinitz called on Vance yesterday afternoon and told reporters later, "I conveyed to the Secretary our strong feeling and concern about it." Dinitz said he was similarly told there has been no shift in U.S. policy. Nevertheless, Dinitz said, "Sometimes even when there isn't a shift, the impression that is created, creates negative consequences, and that is what we are upset (about)."