The basic Democratic commitment to social welfare programs was the overriding reason Reagan administration officials did not see what they expected when they turned on their televisions the Sunday of Memorial Day weekend, setting of this week's climactic negotiations on President Reagan's tax program.

They had expected a Democratic olive branch from House Majority Leader Jim Wright -- an expectation excited by Wright himself two days earlier. Instead, they heard his familiar call for "more [tax] relief to middle-income Americans . . . and to the working poor."

Returning to the White House Tuesday after the holiday weekend, presidential chief of staff James Baker called Republican leaders in Congress: Time is up; is Democratic leaders cannot agree with us by Friday, we will again follow the budget route and make common cause with conservative southern Democrats.

The reason Wright could not buy what the White House thought would be the basis for a bipartisan compromise was future-year annual tax rate reductions of 10 percent, viewed by rank-and-file liberal congressmen as the death warrant for 50 years of social legislation. Yet, it seems inconceivable that Reagan would trim future tax cuts down to Democratic specifications. Thus, despite the hastened pace of consultation, there was no clear way to bridge this immense ideological gap, certainly not by the Friday deadline. That confronts House Democratic leaders with a possible repetition of their budget defeat.

Less than a month ago, those leaders envisioned Democratic ranks reunited in opposition to a Kemp-Roth-style tax rate reduction -- 10 percent a year for three years -- handing Reagan his first real defeat. But there never was any chance Reagan would stubbornly insist on riding Kemp-Roth all the way to oblivion.

In fact, secret administration strategy sessions fixed on only three non-negotiable demands: first, a multi-year bill; second, across-the-board rate cuts, evenly, for both rich and poor; third, some individual tax rate reduction going into effect this year.

That third condition was subject to considerable debate within the White House and the source of trouble with the "boll weevils," the conservative southern Democrats so important in passage of the Reagan budget. The compromise worked out with the southerners would cut individual rates 5 percent effective Oct. 1 and another 10 percent July 1, 1982 (with yet another 10 percent cut a year later). This would be sweetened by assorted tax-cutting goodies popular in the House.

Seeking to avoid a pitched battle on the House floor, Reagan's men wanted to extend the deal beyond the boll weevils to Rep. Dan Rostenkowski, chairman of the House Ways and Means Committee, acting in behalf of regular Democrats. A possible sweetener for Democratic egalitarian sensibilities: lowering the lowest bracket tax rate from 14 percent to 10 percent.

Rostenkowski, not relishing a defeat on his maiden effort as Ways and Means chairman, eyed such a deal. But he was burdened by divided Democratic counsel. Speaker Thomas P. O'Neill supported insistence by younger, more liberal Democratic congressmen to avoid lost revenue for social programs.

On Thursday, May 21, Majority Leader Wright appeared moving toward compromise. In telephone calls to administration officials, he suggested readiness to compromise. He did disclose opposition from Speaker O'Neill and Rep. Richard Bolling, the doughty liberal who heads the House Rules Committee. Nevertheless, word spread around the administration's upper levels that Wright might embrace the compromise package on "Face the Nation" on Sunday.

Wright's non-committal performance reflected decisive rank-and-file Democratic opposition not to the first 5 percent in tax rates but the second and third years of the program. While Rostenkowski cannot swallow these cuts without losing a majority of Democrats, it is those cuts that Ronald Reagan does not want to abandon.

Those were the stakes over breakfast at the Treasury yesterday when Secretary Donald T. Regan hosted Rostenkowski and the Republican Senate Finance Committee chairman, Sen. Robert Dole. Although everybody prefers a quick tax agreement, all are obstructed by the cutting edge of Reagan's economic program: deep, protracted tax rate reduction.

Rostenkowski and Wright cannot accept that cutting edge, viewed by mainline Democrats as a lethal threat to the New Deal, the Great Society and the overriding impulse of their party. Unless Reagan amazes everybody by surrendering, he will again battle House Democratic leaders on the floor, with the odds heavily in favor of the president.