Secretary of State Cyrus Vance described Egypt and Israel yesterday as being on the verge of final agreement on a bilateral peace treaty that will lead into new negotiations for a more general Middle East settlement to include the West Bank territory of the Jordan River.

Vance, who met with Israel Prime Minister Menachem Begin in New York on Thursday, said that "almost all the substantive issues" involved in the three-week-old negotiations in Washington have now been resolved. He said the West Bank issue would be dealt with specificially in a separate document to be exchanged by Israel and Egypt.

Vance's suggestion that a new triumph was at hand for U.S. mediation came at the first general news conference he has held since the wildly fluctuating, on-again off-again talks began here.

Shortly after Vance spoke, Egypt's chief negotiators flew home to Cairo to brief President Anwar Sadat on what appears to be a nearly complete draft treaty, which other diplomatic sources suggested could be initiated by the negotiators within the coming week and sent back to the capitals for final approval.

In contrast to his expressed optimism about the peace treaty, the secretary was insistently noncommittal about a proposal, which, he confirmed, Begin made during their discussion, for a U.S. loan to cover Israeli expenses in withdrawing from the Egyptian Sinai peninsula.

Vance declined to give a figure for the loan, but Begin told reporters in New York Thursday night after meeting Vance that Israel needed $3.3 billion in a 25-year loan, to enable it to relocate military bases and weaponry now in the Sinai back into Israel. Begin's comments contained a strong suggestion that the withdrawal would not be possible unless Washington extended such financial help.

"Obviously that kind of a question would require very careful study," Vance said of the request for a loan. He emphasized that the only U.S. commitment made thus far is for assistance in building two airfields in the Negev desert for Israel to replace airbases being given up in the Sinai.

That commitment was originally intended as a grant, but Israeli sources said yesterday that Begin felt that seeking a larger package as a loan would help stabilize the frequently unsteady relationship between the Carter administration and Begin's government. Israel currently owes the United States about $6 billion.

On other points, Vance:

Indicated the prospects for establishing diplomatic relations with Vietnam have significantly improved through recent exchanges in which the Vietnamese have dropped a demand for a substantial aid package in return for diplomatic ties. The aid demand had blocked previous discussions on normalization, Vance said.

"No decisions, however, have been made with respect to this issue," Vance said.

Committed the United States to continue to refuse to sell weapons to China but said that any other nation approached by the Chinese "must decide for itself." This varied from past U.S. insistence that NATO members also respect an arms embargo against the Chinese.

A Chinese arms-purchasing team is currently in France, and diplomatic sources reported that Soviet Foreign Minister Andrel Gromyko expressed sharp concern to the French during his visit last month about reports that the Chinse are interested in purchasing a long-range missile system from France.

Vance confirmed that the Russians "have raised the question of the sale of weapons to the People's Republic of China not only with us but with many other nations."

Backed away from previous administration predictions that a strategic arms limitation treaty (SALT) agreement with the Soviet Union was likely by the end of the year. "I believe it is still possible it will be done this year, but I don't want to predict it now," Vance said.

He said SALT contacts were now being carried out at the routine delegation level in Geneva and he did not announce any plans to meet with Gromyko to discuss what Vance called "a handful of issues" that are still unsettled in the nuclear arms talks.

Condemned "a clear violation of the borders of Tanzania by Uganda" and said the United States "fully supports the position of President (Julius) Nyerere that the forces of Uganda should be withdrawn immediately" from Tanzania. Uganda claimed this week it has annexed 700 square miles of Tanzanian territory.

Labeled Rhodesian strikes into Zambia an obvious impediment to the holding" of peace talks between Prime Minister Ian Smith's government and the Patriotic Front guerrilla forces. Violence initiated by the guerrilla also has dealth "a real setback" to peace efforts, Vance added.

In Rhodesian, Smith lashed back at sharp criticism from the United States and Britain of raids on Thursday. "I am quite taken aback at the hypocrisy of the two governments," Smith said in claiming that Washington and London have failed yet to respond to his offer last month to put a cease-fire into effect if the guerrillas will agree to it.

The Middle East was the main topic of the news conference and Vance disclose that the troublesome topic of the timing and format of negotiations on the West Bank that are to follow the signing of the Egyptian-Israeli treaty will be dealt with in a separate document.

These details will probably be covered in separate notes that Egypt and Israel will exchange after the treaty be sen to be linked to the A general statement intended to meet Egyptian demands that the treaty to be seen to be linked to the future of the West Bank negotiations is included in the preamble of the draft treaty, the official said.

The departure for Cairo of Acting Foreign Minister Boutros Ghali and Ambassador Osama al-Baz, the chief Egyptian negotiators, left uncertain whether there would be further negotiations here before their return. Israel Foreign Minister Moshe Dayan spent yesterday afternoon at the State Department meeting with Vance's special representative on the Middle East, Ambassador Alfred L. Atherton Jr.

State Department spokesman George Sherman, speaking for the three delgations, said the two Egyptian officials were going to Cairo "for a few days of consulations" about "remaining issues of substance." Defense Minister Ezer Weizman returned to Israel Thursday to make a similar progress report to the Israeli cabinet.