WASHINGTON — WASHINGTON -- In her first Capitol Hill appearance as Social Security commissioner, Shirley Sears Chater got a friendly reception yesterday from a subcommittee that was nevertheless skeptical that a "re-engineering" effort would solve the huge agency's problems. Ms. Chater, who took office Oct. 18, admitted that the backlog of new applications for disability payments and the lack of reviews of disability beneficiaries to see if they remain eligible constitute "the agency's most challenging problem." Acknowledging that she would like to have "more resources," Ms. Chater said that additional funds provided this year by Congress for more workers and computer modernization would not solve the problem. "We will still be fighting a losing battle unless significant changes are made in the way we administer the disability program," she told the Ways and Means Social Security subcommittee. Citing one example of a situation that should be streamlined, Lawrence H. Thompson, the agency's principal deputy commissioner, said it is not uncommon for more than 40 workers to deal with a single disability case file as the application is processed. The agency is beginning what it calls a "re-engineering," which Ms. Chater described as an effort "to fundamentally rethink and radically redesign our business processes as a whole, from start to finish, so that they become more efficient and, as a result, significantly improve SSA's service to the public." With 65,000 employees, the Social Security Administration, headquartered in Woodlawn, touches the lives of most Americans. It mails about 45 million benefit checks monthly, including about 6 million to recipients of disability benefits, and collects payroll taxes from some 135 million workers. It is one of the most closely watched programs on Capitol Hill because members of Congress often hear from constituents who have problems with the agency. Subcommittee members made clear their dissatisfaction with the agency, though they did not blame Ms. Chater. Some, including Democratic Rep. Andrew Jacobs Jr. of Indiana, the chairman, and Rep. Jim Bunning of Kentucky, the senior Republican, said many of the agency's problems would be solved if it were removed from the Department of Health and Human Services and made independent. The Social Security Administration has virtually abandoned reviews of people now on the disability rolls in a desperate effort to cope with the mushrooming claims for new benefits. The backlog of new claims stood at just over 700,000 at the end of September. The Clinton Administration, projecting that the backlog would nearly double to more than 1.3 million by Sept. 30, 1994, unless action were taken, included an extra $120 million in the budget for the fiscal year that began Oct. 1 to deal with the problem. Congress added another $200 million, a figure that would permit the hiring of nearly 5,000 additional workers -- half by the Social Security Administration and half by state agencies that do much of the processing of disability applications, said an aide to the House Appropriations subcommittee that handles the Social Security budget. "We don't expect that with the money we have added that things will get better," the aide said. "It will allow them to tread water." The Social Security Administration must get a waiver from the Office of Management and Budget before it can use the added money to add workers to its payroll -- at a time when the Clinton Administration is talking of cutting 252,000 federal employees as part of Vice President Al Gore's "re-inventing" of the government. But no waiver would be required if it passed the money along to state agencies for the hiring of workers, an agency spokesman said. The agency lost 20 percent of its work force during the Reagan administration as it sought to automate its operations, an effort that has been widely regarded as a failure. It shifted much of its contact with the public to toll-free lines, leaving many people unable to get in touch with the agency and having them wait on hold once they did make contact.