WASHINGTON--The Reagan administration pressed the Senate's Republican majority with some success yesterday to reverse the congressional tide against his $8.5 billion arms sale to Saudia Arabia.

At the same time, the House Foreign Affairs committee voted 28-8 to recommend rejection of the deal.

"I need you, the country and the world need you on this decision," the president was quoted as telling 43 Republican senators at a White House meeting. While Reagan lobbied the Senate, Secretary of State Alexander M. Haig Jr. told reporters at a news conference yesterday that assassinated Egyptian President Anwar Sadat had recently urged approval of the sale, and added that to reject it "would make a mockery of all President Sadat stood for."

After hearing Reagan's appeal, Sen. Alan Simpson (R-Wy) switched from the opposition ranks to support of the sale. The president won a similar turnaround from Sen. Orrin Hatch (R-Utah) on Tuesday. In addition, six previously uncommitted senators declared yesterday they would back the president. All had been considered likely to take that position.

But Reagan's appeal failed to sway at least four Republican opponents of the sale, and Sen. Alan Cranston (D-Ca), a leader of the opposition to the sale, said his vote count still shows 55 senators committed to or against the sale.

"If a snowball was going to roll to change sentiment, it would have rolled yesterday or today," Cranston said.