The major budget alternatives before Congress, as it enters the most crucial phase of this year's battle over spending and taxes, would all cut deeply into domestic social welfare programs, from a minimum of $69 billion over the next three years to a maximum of $124 billion.

Differences on taxes and defense are equally large.

At one end of the spectrum is President Reagan's original plan, which calls for a large defense buildup, relatively small tax increases and big domestic program cuts.

At the other extreme among the five major plans under review are the budget resolution approved by the Democrat-dominated House Budget Committee and a bipartisan alternative put forward by Reps. Les Aspin (D-Wis.), Joel Pritchard (R-Wash.), Leon E. Panetta (D-Calif.) and others.

These call for appreciably smaller defense increases than Reagan does, much larger tax increases and much smaller domestic cuts. A sixth alternative offered by Rep. David R. Obey (D-Wis.) goes even further in the same direction, but is given relatively little chance of House approval.

Between Reagan on the one hand and the House Budget Committee and Aspin-Pritchard-Panetta on the other are the the House Republican leadership plan (called the Michel-Latta plan after GOP leader Robert H. Michel of Illinois and Rep. Delbert L. Latta of Ohio) and the budget resolution that has come out of the Senate.

Both would raise taxes more than the president would, cut his proposed defense budget a little and cut domestic spending less than he would. The Michel-Latta bill is closer to the Reagan figures than the Senate resolution.

Democrats have argued that the president's budget would provide more than is needed for defense, cut too much from crucial social programs like Medicare, welfare and education which were already cut severely in last year's Reagan budget victory, and still create too large a deficit because it would leave undisturbed next year's scheduled third installment of the president's tax cut.

Their alternative would retard defense growth, cut social programs less and increase taxes more, perhaps by postponing the third year of the Reagan cut, to reduce the deficit.

Both the Senate and House Republicans are steering a middle course on these three issues.

None of the plans assumes any cuts in Social Security. The Senate Budget Committee proposal initially did assume $40 billion in Social Security retrenchment from fiscal 1983 to 1985, and the president endorsed this idea, but opposition to Social Security cuts in an election year was so strong that Senate Budget Committee Chairman Pete V. Domenici (R-N.M) simply dropped it.

Here is how various plans line up on key categories, based on comparisons by congressional budget experts using Congressional Budget Office basic figures. Numbers, which are roundedoff, represent the estimated differences between the proposals and what would otherwise be spent on various programs or raised in taxes in fiscal years 1983 to 1985 under current law after adjustment for inflation. On defense, however, the comparison is with what the president requested. Where experts differed on a proposal, figures provided by its author were used:

* The Reagan budget, as most recently reestimated by Capitol Hill budget experts, maintains basically the same defense figures that the president initially sought, would raise $44 billion in new taxes from fiscal 1983 to 1985 (not including certain user fee changes), and would cut "entitlements" or basic benefits such as Medicare, Medicaid, welfare, food stamps, federal pay and cost-of-living adjustments, by $65 billion. In addition, it would cut a big block of other domestic programs (primarily "discretionary" programs in which beneficiaries do not have a legal entitlement to aid and in which outlays are therefore at the government's discretion, such as education and health grants, energy, transportation, natural resources and housing) by about $59 billion. Combined cuts in entitlements and in the other domestic programs would therefore total about $124 billion over fiscal 1983-85.

* Michel-Latta plan: Cuts president's defense proposal $22 billion from 1983 to 1985, raises $95 billion in new taxes, cuts entitlements $63 billion and discretionary domestic spending about $53 billion. Combined domestic entitlement and other cuts: $116 billion.

* Senate plan: Cuts president's defense proposal $22 billion from fiscal 1983 to 1985, raises $101 billion in new taxes, cuts entitlements $67 billion and discretionary domestic programs $28 billion. Combined entitlements and other domestic cuts: $95 billion.

* Aspin-Panetta-Pritchard: Cuts defense $46 billion, raises taxes $135 billion, cuts entitlements $39 billion and discretionary and other domestic spending $32 billion. Combined entitlement and other domestic cuts: $71 billion.

* House Budget Committee plan: Cuts $47 billion in defense, raises $147 billion in new taxes, cuts entitlements about $43 billion and other domestic programs $26 billion. Combined entitlements and domestic cuts: $69 billion.

* Obey plan: Cuts defense $76 billion, raises taxes $232 billion, cuts entitlements $28 billion, cuts other domestic programs $9 billion. Combined entitlement and other domestic cuts: $37 billion from 1983 to 1985.