House-Senate conferees, anxious to cut costs, voted yesterday to restrict new starts on subsidized housing for the poor and to authorize higher rents for the projects.

The decision ended weeks of squabbling between Rep. Thomas L. Ashley (D-Ohio) and Sen. William Proxmire (D-Wis.) over the low-rent public housing and rent subsidies programs for the poor.

The two programs together are one of the nation's biggest welfare programs, already costing $5.5 billion a year.

Proxmire, backed by Jake Garn (R-Utah), and a majority of other Senate conferees, demanded that the total number of new public housing and low-rent-subsidy units authorized for 1980 be held to about 265,000 units -- the lowest in recent years and the figure backed by the Carter administration.

Ashley, objecting, said the subsidy programs, which apply to apartment for the poor, help the most desperately needy in society. A few years ago, he said, over 400,000 new units were approved, then the figure dropped in fiscal 1979 to about 327,000 and now it was proposed that 265,000 be added to the number previously authorized over the years.

"Let's bear in mind what we have done to people who can't afford housing in the name of belt-tightening," he argued at one recent session.

However, conferees on the housing authorization bill finally adopted the 265,000 figure. Proxmire pointed out that the Appropriations committees have already made clear they won't go beyond 265,000 -- which is nearly a 10 percent increase.

In a second dispute, conferees agreed that future tenants in low-rent public housing and subsidized housing apartments may be required to pay up to 30 percent of their incomes as rent, instead of the current 25 percent. The increase wouldn't apply to the lowest-income tenants or to those already in the apartments -- only to those who move in next Jan. 1.

Ashley and Sen. Harrison A. Williams (D-N.J.), argued that a rent increase to 30 percent would be a cruel added burden to impose on very low-income people. But Proxmire said that even at 30 percent, the new tenants would be paying less in subsidized housing than when they were living in commercial housing.

Proxmire argued that by collecting higher rents from some, the government would be able to use the extra money to create added units and help more families.

On a third issue -- the eligibility rules to get into the subsidized apartments -- Ashley prevailed. Under current law, a family can qualify for the low-rent subsidy housing if its income is 80 percent of the median family income in the area or less. (The nationwide median family income is about $16,000.)

The Senate proposed to tighten this rule by lowering the cutoff to 70 percent, so that only the poorest families would be eligible.

However, Ashley and the administration opposed this change, arguing that people at 80 percent are still needy, and that using the higher cutoff would allow a better mix between very poor and moderately poor families. Senate conferees agreed to keep the 80 percent figure in a compromise after the House took the 265,000-unit limit and the rent rise.

In both low-rent public housing and rental subsidies for private housing, the tenant pays a rental amount based on his or her capacity to pay, as determined by the government, and the United States puts up the difference between the tenant's payment and that actual rent.