Public support for the Reagan economic program, regarded as a major factor in congressional implementation of most of the president's budget requests in 1981 and 1982, has largely evaporated, according to the findings of a Washington Post-ABC News poll.

In sharp contrast to those years, most citizens now oppose key aspects of Reagan's budget proposals.

A majority of the public, for example, is ready to forgo the 10 percent cut in marginal income tax rates scheduled for July, although Reagan says he is adamant in his refusal to delay or eliminate that reduction. A majority also favors cutting military spending, but not social programs, to reduce the national debt.

And a majority favors establishing a jobs program even if that increases the deficit. On each issue, the majority view is in direct opposition to the Reagan administration proposals.

Politically, one result of this massive shift in the national mood will be to make it easier for members of Congress to oppose the president. Repeatedly during Reagan's first two years, moderate Republicans and many Democrats either voted for his proposals or failed to fight them forcefully, saying they had to bow to the president's "mandate" from the public.

Some of the findings from the Post-ABC News poll, in which 1,510 people were interviewed by telephone from Jan. 18 to Jan. 23:

* By 55 to 39 percent, a majority favors reducing the budget deficit by cancelling the 10 percent income tax cut set for July 1. By 63 to 32 percent, the public rejects Reagan's contention that the tax cut will help improve the economy and create new jobs. At the same time, however, the public opposes by 2 to 1 any tax increase to reduce the deficit.

* A majority of 59 to 37 percent favors cutting military spending to reduce the deficit, with 4 percent expressing no opinion. In contrast, when Reagan's budget was before Congress last February, a Post-ABC News poll found cuts in military spending opposed by 53 to 41 percent.

* By 52 to 44 percent, the public opposes cutting spending on social programs to reduce the debt, despite being told by Post-ABC News interviewers that "financial experts say the next government budget will have the largest deficit in history." A similar majority opposed cuts in social programs last year, after supporting them in 1981.

* By 51 to 42 percent, according to the poll, citizens support government "spending to create new jobs, even if that means higher budget deficits." graphics/chart: THE WASHINGTON POST/ABC NEWS POLL By Kathy Junhjohann for TWP