President Carter disclosed yesterday that most of the important issues in the Panama Canal negotiations have been resolved and expressed hope that a new treaty on the waterway can be signed with Panama this summer.

Speaking at a news conference, Carter identified the financial issue of payments to Panama as a serious disagreement remaining. And he noted that even when full agreement is reached and a treaty signed, a major effort will be required to obtain congressional approval.

According to informed sources, the tentative accord calls for Panama to take legal jurisdiction of the canal zone within three years and to assume a gradually larger role in operation and defense of the canal until it is turned over completely by the United States by Dec. 31, 1999.

A separate but closely related U.S. Panamanian treaty, which other nations may also sign, is reported to pledge open and nondiscriminatory access to the canal even after Panama takes control. This document is said to imply - but not to state explicitly- a U.S. right to intervene in case open access should be denied.

In a letter sent to Carter yesterday and made public by Sen. Jesse Helms (R-N.C.), retired Adms. George Anderson, Arleigh A. Burke, Robert B. Carney and Thomas H. Moorer - all former chiefs of naval operations - urged that the United States "retain full sovereign control" over the canal and canal zone for security reasons.

Denoting military command support for the planned treaty, Gen. George Brown, chairman of the Joint Chiefs of Staff, and Army Chief of Staff Gen. Bernard W. Rogers have participated with U.S. treaty negotiators Ellsworth Bunker and Sol Linowitz in briefings for more than half of the Senate and key members of the House of Representatives. Ratification of a treaty requires a two-thirds vote of the Senate, and in this case implementing legislation from the House and Senate would also be needed.

Panamanian negotiators are said to have mentioned figures as high as $1 billion in payments for continued U.S. control over the canal during the next two decades, and some reports say serious demands have been made for several hundred million dollars. The United States is prepared to offer much less and is insisting, as Carter suggested yesterday, that the payments to Panama be made from portions of the tolls collected from the ships passing through the waterway.

Strong opposition from some members of Congress and heavy mail to Congress and the executive branch against a "giveaway" of the canal suggests that Carter faces a tough political battle for approval. Negotiator Linowitz told a State Department briefing Tuesday. "The grim fact is the American people are not yet ready to support a new treaty. They are grossly uninformed about it."

Carter has pledged to present the case for a treaty in a broadcast "fireside chat" at the right moment. He is being informed daily on the negotiations and said yesterday he is devoting a lot of time to them. Carter said it is his judgment that Brig. Gen. Omar Torrijos, Panama's governmental leader, also would like to conclude a new treaty this summer.

In his news conference, which was dominated by military and diplomatic topics, Carter also said:

He would welcome a chance to meet this year with Soviet leader Leonid I. Brezhnev but the time and place for such a meeting are yet to be worked out. While saying there are major obstacles to proposed agreements on strategic arms limitations, a comprehensive nuclear test ban and Indian Ocean demilitarization, Carter denied that Soviet-American relations are deteriorating.

Last Friday, Carter told a group of editors in a White House meeting that "a surprising adverse reaction" in Russia to his human rights campaign has caused a greater obstacle than he expected to friendly pursuits such as the SALT talks. Yesterday he said he saw no relationship between his human rights stand and the SALT negotiations and doubted whether the Soviets see any connection. In any case he said, "I don't have any regrets" about the human rights positions and would not change them in retrospect.

He hopes to establish full diplomatic relations with China while making sure that "the peaceful lives" of people on the island of Taiwan are maintained. He said he hopes that mainland China and Taiwan can work out their differences but gave no indication of how the United States will handle the problem in the likely event that the two sides are unwilling to do so.

He plans to withhold further comment on the Arab Israeli dispute until the new Israeli prime minister, Menachem Begin, visits Washington in mid-July. Carter defended his public statements on the elements of a Middle East peace agreement, saying the open discussion has encouraged the Arabs and Israel to understand feelings on the other side and address the basic questions. Carter said he will seek to be an intermediary in peace efforts without any abandonment of "our deep and permanent commitment to Israel" and that he had so informed Arab leaders.

He hopes and Saudi Arabia hopes that the present crude oil price level of most Organization of Petroleum Exporting Countries will be frozen at least through 1978. Carter said Saudi Crown Prince Fahd, on a visit here last month, had confided that Saudi prices are likely to be raised somewhat to match the present level of other OPEC countries, thus ending months of disunity within the oil cartel.

While the United States could accommodate additional oil price hikes, "I think the prices are too high," Carter said. He said the United States is using "our good offices" to hold down additional increases in oil prices. No details were given.