Congressional Democrats and the White House appeared to break the impasse last night on a compensation package for anyone harmed by the smallpox vaccine, a move that should alleviate concerns that health care workers have expressed about volunteering for the controversial immunization program.

Under the tentative agreement, anyone permanently disabled as a result of inoculation would be eligible for up to $50,000 a year in lost wages, said Senate aides involved in the negotiations. People who were partly disabled could collect the same benefit up to a lifetime maximum of $262,000.

The government would also pay death benefits of $262,000 to a spouse and would offer surviving children the option of that flat payment or $50,000 annually until they turn 18.

When President Bush called for millions of health care workers and emergency responders to be immunized against smallpox, the administration did not provide any compensation for the small number of individuals expected to have severe complications.

Many nurses and doctors -- along with Health and Human Services Secretary Tommy G. Thompson -- said the lack of compensation was a primary reason why so few people have signed up for the program. About 31,000 medical personnel have been inoculated, far below the target of 450,000.

After the Republican-controlled House roundly defeated the administration bill proposing a more limited compensation package last week, White House aides joined intense negotiations with Senate leaders of both parties.

Many details of the package were being finalized last night, although aides for the administration and lawmakers expressed confidence that the broad outlines would hold.

"We're pretty close," HHS spokesman Bill Pierce said.

About $45 million has been set aside for the program, tucked into the emergency spending bill for the war in Iraq.

"The compromise that we have reached tonight provides the nation's health care workers with an effective compensation program that will give them the confidence they need to participate in the smallpox vaccination program," said Sen. Edward M. Kennedy (D-Mass.), who led the fight against the administration plan in the Senate. "They deserve nothing less, and our nation's security demands it."

Thompson, who began pressing the White House for a compensation package last summer, has predicted that participation in the program will soar once a package is put in place. But sources involved in the discussions said the administration has revised its projections downward from 10 million inoculated to 4 million and finally 2 million.

After a particularly rancorous committee fight over the bill's language last week, Senate staff members and White House aides spent Saturday attempting to resolve their differences. The outlines of the final agreement were sealed Wednesday night in a telephone call between White House Chief of Staff Andrew H. Card Jr. and Kennedy, his home state senator.