The special House welfare subcommittee yesterday approved president Carter's welfare "reform" plan about as he proposed it, but only fter a much less costly aternative was almost approved.

The subcommittee approved the Carter plan 23 to 6, but first - in perhaps its more revaling vote - it defeated 16 to 13 the alternative offered by Rep. Al Uliman (D-Ore.).

WHile the votes were a victory for the President, they also indicated that his plan has a mine field of opposition to cross and that its chances of passage this year are uncertain.

The bill must now obtain approval from the Ways and Means Committee, whose chairman, Ullman, regards it as too costly and complex; from the House Agriculture Committee, whose members elimination of food stamps; and from the Education and Labor Committee.

Then it would have to passed on the House floor, where conservatives would be sure to criticize its minimum income provisions as a disincentive to work, and blast it for its cost.

Agriculture Committe Chairman Thomas S. Foley (D-Wash.), an opponent, said the legislation "cannot possibly pass the Congress - cannot possibly pass the House - in anything like its pesent form."

The Congressional Budget Office has estimated that in 1982, when the legislation would go fully into effect, it would cost the federal government $49 billion - $21 billion more than if existing programs were continued. This price tag could be a problem in the House. If it ultimately passes the House, the legislation would face similar opposition in the Senate Finance Committee, whose chairman, Russell B. Long (D-La.), has already made plain he dislikes it.

Subcommittee Chairman James C. Corman (D-Calif.) is aware of these problems, but yesterday he was all smiles as the subcommittee completed two months of work.

Unification of all cash welfare programs and elimination of food stamps. Beneficiaries would receive extra cash payments to compensate for food stamp loss. The program would take care to fhose unable to work ans supplement the wages of all low-income persons.

Establishment of a munimum-come guarantee for every poor person, including several groups (young, childless couples and single persons, unemployed fathers) previously ineligible for welfare in some or all states. For those without any other income, the minimum annual federal welfare payment (including food stamp compensation) would by $2,500 for an aged, blind or diabled person ($3,750 for a couple; $1,100 for an able-bodied young person without children ($2,200 a couple), and varying amounts for families depending on their size ($4,200 for a family of four). (The states could supplement these figures if they chose.) If any of these persons worked, their benefits would phase out as their other income climbed. For a family of four at $4,200 in benefits, welfare payments would phase out at $8,400 in earnings.

The requirement that any young able-bodied person without small children seek a job. He or she would receive benefits only if unable to obtain a job. The federal government would fund over 1 million special public service employment jobs annually, at salaries ranging from $7,000 to $10,500, depending on local wage scales in ordinary employment. Employable welfare clients unable to find a job elsewhere would have to take a public service job if it were available in their area or lose - 9:30 a.m. Open. Fossil & Nuclear Energy Res., Devel