President Carter's welfare plan ran into some sharp criticism yesterday, when a group of Republican conservatives denounced it as "a disaster for the poor, the needy and the taxpayers."

Robert B. Carleson, who was commissioner of welfare under Ronald Reagan in California and Richard M. Nixon and Gerald R. Ford in Washington, ripped the Carter proposal at a press conference called by the American Conservative Union.

Carleson and Rep. Philip M. Crane (R-Ill.), the chairman of the ACU, said the Carter plan "represents a massive enlargement of the nation's welfare system that will add millions to the welfare rolls."

They also said that, contrary to Carter's rhetoric, the plan is anti-family, anti-work and a potential budgetbuster.

Crane and Carleson said they would present, later this year, an alternative proposal that would turn welfare back to the states and reduce the size of the welfare rolls. Their rhetoric suggested that sharp partisan battles may be ahead when Congress takes up the Carter proposal,

Administration officials quarreled with some of the examples cited at the ACU press conference, but they do not dispute that Carter's plan will be more expensive and inclusive than existing welfare programs.

One feature - the increase in the so-called earned-income tax credit - would benefit 12 million families not aided now among the "working poor," including some with incomes as high as $156,000 a year, officials said.

As an example of what it called the anti-work and anti-family features of the Carter plan, the ACU officials cited the case of a father with a family including a small child, who refuses to take a government-subsidized job under the Carter program and, instead, abandons the family.

"By leaving the family," they said, "he would make them eligible in the "not expected to work" category, thereby increasing family benefits to $4,200 a year, plus state supplements.He then could apply for benefits for himself as an individual and receive an additional $1,100 a year. Because the 1.4 million subsidized job slots are reserved for families, he could not be offered or required to accept one, and would therefore continue to receive the $1,100 benefits, plus any state supplements."

A Health, Education and Welfare Department official commented that the man in question would get his $1,100 only if no job could be found through the government "job search program."

As for his family, the $4,200 it would receive by his desertion is far less than it would receive if he stayed homne and worked. "If he stays with his wife and family," said a HEW official, "he's guaranteed a job that pays $5,500 a year, and the family is eligible for an additional $2,050 in federal benefits, or a total of $7,500. I call that a pro-family program

Meantime, Sen. William Proxmire (D-Wis.) delayed the start of his vacation to hold a hearing of his Senate Banking, Housing and Urban Affairs Committee, at which a parade of witnesses warned against any tampering with housing subsidies as part of welfare overhaul.

The Carter administration had considered and rejected "cashing-out" some existing housing subsidies to help pay for higher welfare benefits, but Proxmire said he expected the issue to be raised "again and again" as Congress considers the welfare issue.

With Proxmire's encouragement, Leon Weiner, president of the National Housing Conference, and four other witnesses recited the arguments against reducing housing benefits for welfare recipients.

Weiner argued that it made no more sense to increase cash payments to the poor and tell them to obtain their own housing than it would be to "divide up the defense budget among 200 million Americans and tell each of them to go buy yourself some defense."

Sen. Richard G. Lugar (R-Ind.), the only other senator present, spoiled the unanimity of views by suggesting that the claim to exempt housing benefits from welfare changes was "a case of special pleading."

He warned the Witnesses they will have to make "a very strong case" to avoid housing subsidy cutbacks when the administration rviews its budget for fiscal 1979.