The White House announced yesterday that President Carter plans to send Congress his controversial Middle East arms sale package by tomorrow, despite new opposition from an influential senator.

Press secretary Jody Powell, making the announcement, left open the possibility of a brief delay if a negotiated agreement to head off a political battle seemed near. But White House sources said Carter is strongly inclined to go ahead. "He's had a bellyful" of the arguments about the proposed sales, said an official. "We think the momentum is with us."

In a meeting with Carter and in a letter to Secretary of State Cyrus R. Vance, Sen. Frank Church (D-Idaho) argued yesterday that the proposed sales of sophisticated warplanes to Israel, Egypt and Saudi Arabia should be considered as separate deals rather than being linked. The ranking Democrat on the Senate Foreign Relations Committee and its likely chairman starting next January, Church said the attempt to "package" the sales would set a precedent that would thwart objective congressional review.

Church, in a telephone interview, said he believes that Foreign Relations Committee will vote to disapprove the proposed sales of jets to all three countries as a protest against the "linkage" if Carter presents them as a package as now planned. Church said he had stated his objections to Carter and Vance "so they can be forewarned."

Administration sources said some negotiations are going on with members of Congress about ways to forestall the threatened confrontation. But both executive and congressional sources suggested that the chances for agreement before tomorrow are not strong.

Powell emphasized yesterday that Carter will not agree to scale back the size of the planned sales to the three countries. He reiterated that the president is determined to win approval of all the sales or to scrap the entire package.

Among the matters being discussed for negotiation are assurances that the Saudi jets would not be based near Israel, assurance that bomb racks and offensive equipment would not be sold, and arrangements to stretch out the delivery dates for the planes. It is unclear that any of these concessions - even if acceptable to Saudi Arabia - would satisfy opponents of the sale.

Under the law, it takes a majority vote to both houses of Congress within 30 days of submission to stop a proposed arms sale. Carter fixed tomorrow, April 26, as the time for submission because it is the last day the sales could be sent to Congress without the 30-day period expiring during the Memorial Day recess.

Vance has scheduled a meeting tomorrow morning with several influential senators to discuss the arms sale package. Some sources suggested this may be the last chance for an agreement that could avert a bruising battle between the Carter administration and pro-Israeli forces on Capitol Hill.

Israel has strongly opposed the proposed sale to Saudi Arabia of 60 F15 jets, which would be by far the most sophisticated fighter acquired by that country. Israeli officials have been notably less fervent in opposition to the sale to Egypt of 50 F5s, a considerably less powerful warplane.

Israel and its congressional supporters have insisted that its planned purchase of 15 F15s and 75 F16s should not be linked to the transactions with the Arab states, saying that the United States has an independent commitment to supply Israeli needs. In recent days, some in Israel - including the retiring chief of staff, Gen. Mordechai Gur - have said that Israel would be better off to jettison the entire group of sales rather than permit the Saudi F15 acquisition to go through.

Carter, Vance and other senior officials will have a firsthand exposure to Israeli views in the next week. Israeli Foreign Minister Moshe Dayan is due here for lengthy and substantive talks tomorrow and Thursday with Vance on major issues in the stalled Egyptian-Israel peace negotiations.

Next Monday Israeli Prime Minister Menachem Begin is to be guest of honor at the White House at a reception given by Carter to celebrate the 30th anniversary of the founding of the state of Israel. From 600 to 1,000 American Jewish leaders are being invited. Lists of names for invitations are being solicited from some of the organizations that are leading the lobby fight against the Middle East arms package.

Begin is scheduled to travel to Los Angeles, Chicago and New York for long-planned celebrations of Israel's founding. His stopover at the White House and perhaps the State Department is being described by U.S. officials as more in the nature of ceremonial calls than substantive discussion. But this could change, they said, if the Dayan talks produce a new Israeli position.