The House brushed aside two of the three alternatives to President Reagan's austerity budget yesterday as Speaker Thomas P. O'Neill Jr. (D-Mass.) conceded that "only the Lord himself" could now block approval of Reagan's spending cuts.

A proposal from the Congressional Black Caucus to forestall massive spending cuts for social programs and to target tax cuts toward low- to moderate-income people was rejected, 356 to 69.

Then the House, voting 303 to 119, turned down a proposal from Rep. David R. Obey (D-Wis.) that would also have shielded money domestic programs from cuts proposed by Reagan and deferred any tax cut for individuals until 1983.

Both the Black Caucus and Obey contended their proposals would have balanced the 1982 budget, unlike the two main spending blueprints recommended by Reagan and House Decocratic leaders.

A final vote on Reagan's budget and the Democratic leadership's counterproposal was deferred until today, but Democratic leaders clearly held out little if any hope for their proposal in the Democratic-controlled House. o

"Only the Lord himself could save this one," O'Neill told reporters, attributing an expected surge of Democratic defections to Reagan's popularity and to a pervasive view that Congress should "give the American people what the president has asked for."

What little hope the Democrats had that enough Republicans might cross over to turn the tide their way appeared to fizzle when nine previously uncommitteed GOP members announced they intend to vote for Reagan's budget. u

But the Republicans, mostly from the Northeast and Midwest, also asserted that their budget vote would not bind their future actions and vowed to "shift some of the defense increase [in the Reagan budget] to social problems" -- posing problems for Reagan in the future as he seeks to keep his fiscal discipline from collapsing under the weight of popular spending programs.

With only one identified Republican defector, Rep. James M. Jeffords (Vt.), 27 Democratic crossovers could carry the day for Reagan. Conservative Democrats have been saying for several days that the president will get many more votes than that for his budget.

Even the White House, which played a cautious game as Reagan personally lobbied about 60 wavering Democratic and Republican lawmakers over the past week, came closer than ever before to anticipating victory. "We feel today that the tide is running our way," said deputy press secretary Larry Speakes.

The choice before the House today will be a revised version of the Reagan budget drafted with White House blessing by Reps. Phil Gramm (D-Tex.) and Delbert Latta (R-Ohio) and a less drastic Democratic alternative proposed by the House Budge Committee. The budget will set preliminary spending targets for fiscal 1982 and also require congressional committees to make spending cuts to meet these targets.

The Democrats' budget would cut spending for social programs by about $7 billion less than the gramm-Latta proposal, which cuts even deeper into domestic spending than Reagan had recommended. It also includes a smaller tax cut than Gramm-Latta, which would accommodate the full three-year, across-the-board tax cut proposed by Reagan.

The Democrats' draft totals $713.6 billion, compared with $688.8 billion for the Gramm-Latta budget. Its deficit would be smaller, $24.7 billion compared with $31 billion for Gramm-Latta. However, the two proposals are based on different economic assumptions, making numerical comparisons difficult.

By contrast, the 18-member Congressional Black Caucus said its proposal would produce a balanced budget, achieved in part by closing a number of so-called tax "loopholes" and thereby raising revenues to offset the caucus' other tax and spending proposals.

"Our proposal is to reduce inflation with compassion," said caucus chairman Walter E. Fauntroy (D-D.C.) during more than five hours of debate on his foredoomed proposal.

"The course the House is proceeding on is economically, politically and morally wrong, and we in the Congressional Black Caucus will not support this insanity," said Rep. william Clay (D-Mo.). "We would rather lose in a cause that is morally right."

Among Washington-area members, only Rep. Michael Barnes (D-Md.) voted for the Obey proposal. None voted for the Black Caucus budget.

While O'Neill all but conceded defeat for the Democrats' counterproposal, he continued to criticize the Reagan budget in harsh terms, calling it a "brutal change in the system of America" and saying the budget fight has prompted a "bitterness out there on both sides [of the aisle] that I've never seen before."

O'Neill said he thought the Reagan budget would send inflation and interest rates "through the ceiling," and added with acerbity, "I hope the 90 percent of the economists who say the president is wrong are wrong."

Meanwhile, the Democrats, in a rear-guard action against the Gramm-Latta budget, complained that it contained a revised spending ceiling for fiscal 1981 that is too low to accommodate necessary spending for the rest of the year.

As a result, the Budget Committee refused, for the time being at least, to recommend a waiver to permit a vote on $19.1 billion in supplemental spending for this year that Reagan wants.

The Democrats contend that the $660 billion final spending ceiling for 1981 that is envisioned as part of the Gramm-Latta budget for 1982 is $500 million below what spending would actually be if the supplemental appropriation is approved.

Republicans disagreed, contending that the administration intends to spend no more than the budget would allow.