Congress this week takes up President Reagan's proposed sale of missiles to Saudi Arabia, with foes of the sale claiming that they have a growing majority in both houses committed to vote against the sale.

But a presidential veto of a congressional resolution to block the sale is considered certain, and it was unclear yesterday whether both houses can muster the two-thirds majority necessary to override a veto.

Reagan submitted the arms sale proposal to Congress April 30, and by law Congress has 30 days to reject it. The time for action runs out on Thursday. Although Congress has forced delays in arms sales in the past, rejection of a sale would be unprecedented.

In the Senate, which could take up the issue as early as today, aides to Sen. Alan Cranston (D-Calif.) said that 64 senators have joined Cranston in signing a resolution of disapproval, with the possibility of getting 66 or 67 votes for the resolution and a veto override. It would take 67 votes to override a veto with all senators present.

But the issue is caught up in a dispute over domestic gun control legislation and Senate Majority Leader Robert J. Dole (R-Kan.) refuses to schedule a vote until he has assurances that lawmakers who oppose both the gun measure and the Saudi sale will not try to block or further delay the gun bill.

At issue is legislation easing federal gun control laws. Both houses have approved separate versions of the gun measure and Senate advocates of the bill want the Senate to accept the House version, thereby avoiding obstacles in a conference. Sources said late yesterday that the dispute is nearing a solution and a vote is likely on Wednesday.

In the House, where a vote on the Saudi arms package is expected Wednesday, Rep. Mel Levine (D-Calif.) said that opponents of the sale number about 290, or roughly two-thirds of the House. With all members voting, it would take 289 votes to override a veto.

Although Reagan is expected to await final congressional action before going ahead with the sale even if the deadline passes, failure of either house to override a veto would permit the sale to proceed.

The sale involves $354 million in antiaircraft and other missiles, roughly one-third of the initial Saudi request. The administration pared down the size of the sale to meet domestic objections, including fears that the weapons might fall into the hands of terrorists.

Israel and its supporters in the United States oppose the sale but have not actively opposed it, as they have done in the past, reportedly to save political capital for a fight later in the year against the sale of airborne warning and control system (AWACS) aircraft to the Saudis.