As state-subsidized health care for 31,000 legal immigrants lapsed Tuesday, the result of budget cuts imposed by the Legislature, advocates for a single-payer health care system blasted the cuts as “discriminatory” and said a backup plan endorsed Monday by the Patrick administration could leave them worse off than if they relied on a state fund for the uninsured.

“It’s deplorable,” said Dr. L. Toni Lewis, president of the Committee of Interns and Residents for Service Employees International Union, speaking at a press conference in the State House’s Nurses Hall.

Officials of the Massachusetts Nurses Association, the National Association of Social Workers, immigrant advocacy groups and labor unions said the Legislature should have made cuts across the board, rather than singling out the 31,000 immigrants. Known as “aliens with special status,” these immigrants are ineligible for federal matching benefits because they have been in the country for less than five years.

Rep. Marie St. Fleur (D-Dorchester) said the Massachusetts State Constitution forbids discrimination based on immigration status.

“If we go down the slippery slope of making decisions about who we think should be covered, we should take a step back,” she said.

St. Fleur said that even if the immigrants in question aren’t eligible to vote, their family members and friends should let lawmakers know “there will be a price” if they support policies that disadvantage immigrants.

Lawmakers cut coverage for the immigrants, estimated to cost $130 million this fiscal year, to help balance this year’s budget. Gov. Deval Patrick countered, seeking to fund coverage at $70 million, a figure lawmakers reduced further to $40 million. Legislators said they made the cuts because without them, other essential services for vulnerable populations would need to be cut further.

The administration announced Tuesday a deal with CeltiCare, a new Boston-based insurer, to provide coverage for most basic health services – excluding skilled nursing, dental, vision and hospice care – for the immigrants. The immigrants would be enrolled in the new plan on a rolling basis beginning Oct. 1, with all slated to be enrolled by Dec. 1. In the interim, the uninsured immigrants would have their care funded by the state’s Health Safety Net Trust Fund, a fund that covers certain services for the uninsured.

Benjamin Day, executive director of the Boston chapter of Physicians for a National Health Program, which organized the press conference, said the scaled-back plan for the immigrants could actually provide worse coverage than the immigrants would receive from the Health Safety Net. He cited increased co-payments for services like brand-name medication and emergency care, which the immigrants will see with CeltiCare.

At the press conference in the capitol’s Nurses Hall, Physicians for a National Health Program also gathered 500 signatures of doctors and health care professionals calling for “a single payer reform” and to “fully restore funding for the 30,000 immigrants who face imminent exclusion.”

Opponents of single-payer health care argue that it places bureaucratic barriers between patients and care, requires government involvement in health care decisions, and imposes too great a strain on public finances.