Four senators asked the Interior Department yesterday not to go ahead with a proposed settlement of a lawsuit filed by the Westlands Water District in California until the interior secretary answers questions about it.

In a letter to Interior Secretary Donald P. Hodel, the senators asked whether the settlement would continue the unauthorized federal irrigation water supply to 156,000 acres and whether the public would get a chance to comment on the proposed settlement.

Interior Department spokesman Carl Gagliardi said he was unaware of any plans to publish the settlement before Hodel decides whether to approve it.

The senators were Democrats William Proxmire (Wis.) and Howard M. Metzenbaum (Ohio) and Republicans Richard G. Lugar (Ind.) and Gordon J. Humphrey (N.H.).

The Westlands district sued the department in 1978 to force its Bureau of Reclamation to make a permanent contract to replace temporary agreements supplying water to the disputed acreage.

Former Interior secretary James G. Watt concluded that the water could not be provided without congressional authorization.

The senators said the 1982 Reclamation Reform Act required that new water contracts and amendments to existing contracts be open to public participation, and asked Hodel whether he intended to submit the Westlands agreement "for public scrutiny" before approving it.

The group of senators pointed to news reports indicating that "the agreement will provide water to Westlands past the year 2000 at less than $10 an acre foot, a fraction of its actual cost . . . . What is the justification for such a generous subsidy?"

They also asked whether the agreement called for elimination of a projected $70 million deficit in Westlands' repayments to the federal government and whether the agreement addressed Westlands' responsibility for selenium contamination of the Kesterson Wildlife Refuge by irrigation runoff water. The senators also asked whether any environmental impact statements had been prepared.