The House of Representatives, with the help of right-wing Democrats, last week adopted a Republican budget plan that purports to hold the fiscal 1983 deficit to $99.3 billion. The conservatives who pushed the budget through were determined to get the deficit under $100 billion, while preserving the final stage of the Kemp-Roth personal tax cut. The route they chose amounts to an unconscionable assault on social programs that affect the poorest.

"It's a venal, vicious attack on the working poor," says Rep. David Obey (D-Wis.) In fact, the House cuts go far beyond the outer limits of what responsible Republicans in the Senate were willing to vote for.

The financial markets, to be sure, heaved a sigh of relief, assuming-- cynically but not unreasonably--that since the Senate had passed a budget showing a deficit of about $116 billion, a conference committee would split the difference, which would mean a budget deficit of $108 billion or so. That certainly is more palatable to financial markets than the $182 billion worth of red ink that until then had been the prospect.

But before anyone gets euphoric, some cautions are in order. The House version of the budget is not a detailed blueprint: it reduces the prospective deficit by setting unspecified "goals" for raising taxes and without defining how the steep slashes in non-defense spending are to be accomplished. As Obey says, the budget is a total phony: the "cuts" go far beyond what the operating committees in the House would dare vote for.

If the House were actually to do what the new Republican budget calls for, the result will be massive reductions in social and welfare programs that will hit hard at Medicaid, food stamps and cash programs designed to help the most disadvantaged persons in American society.

Despite repeated claims by the administration that these programs are not being cut--that they merely will increase at a lower rate--the fact is that coming on top of the budget cuts voted last year, the House bill would cut these programs about 30 percent below the levels projected before Ronald Reagan took office.

Examples of the impact over three years:

Medicaid: the House budget cuts $6.6 billion, more than three times the Senate Republican reduction, in effect shifting this burden to the states that do not have the resources to pick up the difference. And as Obey points out, the states and local governments have not yet fully felt the impact of all of last year's budget cuts.

Food Stamps and Child Nutrition: The House bill cuts $7.05 billion for food stamps, and $600 million from child nutrition programs, more than double the Senate slashes. By redefining eligibility, the House bill would reduce food stamp benefits for all 22 million now receiving them, including 500,000 elderly and disabled persons-- some of whom would be completely removed from the rolls.

Cash Programs, including Aid to Families With Dependent Children: For these and related programs, the House budget slashes $3.4 billion, compared with $1.5 billion in Senate cuts. Among other ill-considered moves: a reduction in school breakfast and child-care feeding programs that provide a free or reduced-price meal for 4 million children. Some 80 percent of these kids are poor.

Medicare: Here, the House bill would cut $11.5 billion, or less than the Senate bill's $18 billion. But no one spells out how this money would be saved. The National Council for Senior Citizens says $3 billion of the reduction would represent higher out-of-pocket costs for the elderly to pay for primary health care and physicians' fees.

On the tax side of the ledger, the Senate promised it would raise taxes by $108.3 billion, the House by $98.3 billion. But neither said how it would raise taxes, except to assure that it wouldn't touch that holy of holies, the third year of the Kemp-Roth personal tax cut.

But the money would have to come from somewhere, much from taxes that would fall on low- and middle-income persons, through a variety of excise taxes --including liquor and tobacco-- and some form of energy tax. There also may be a new surtax on individual income. But there is little likelihood that the 20 percent limit on capital gains, or the 50 percent maximum rate on individual income, both of which benefit the upper- income brackets, will be touched.

The Republican budgets, in a real sense, whittle the deficits down at the expense of the poor while leaving last year's huge tax cuts for the rich just about unchanged. The defense budget is still a giant. The vaunted "safety net" that Reagan once promised to defend will be shot full of holes. If the winning Republicans in the House looked glum at the end of the vote last week, while the Democrats smiled, as my colleague Albert Hunt said last Friday on "Washington Week in Review," it's not hard to figure out why.