As senators paraded before the television cameras last Wednesday in a struggle for the political high ground on national health insurance, an aide worked behind the scenes to draft the Republican bill.

She met every day last week with Richard G. Darman, the White House budget director, and with the chief sponsors of the legislation: Senators Bob Dole of Kansas, the minority leader; John H. Chafee of Rhode Island; Dave Durenberger of Minnesota, and John McCain of Arizona. When the bill was announced at a news conference on Thursday, television viewers saw several lawmakers take credit, but they were given no hint of the efforts of Sheila Burke, Mr. Dole's chief of staff. The cult of anonymity of Congressional aides remained intact.

The 40-year-old Ms. Burke, who earns $88,000 a year, is one of the most influential of more than 19,000 Congressional staff members on Capitol Hill, of whom 7,200 work in the Senate and 12,150 work in the House. The majority are on lawmakers' personal staffs, and include legislative aides and administrative assistants as well as secretaries and clerks. Most of their work is virtually invisible except to a handful of Washington insiders, but every once in a while circumstances conspire to place them in the spotlight.

Television viewers of the confirmation hearings for Justice Clarence Thomas, for example, saw a cadre of Congressional aides sitting behind the Senators, whispering advice and handing their bosses sheets of questions. Bloated and Abused?

President Bush focused perhaps unwanted attention on them last month when he criticized Congress for having what he suggested was a bloated staff of 40,000 workers. In fact, when the Library of Congress, Capitol Police, the General Accounting Office and other support systems are included, the number comes to a little more than 31,000 -- about the same as a decade ago.

The "Hill people," as they are known in Washington, also made headlines when the Senate last month agreed to extend job discrimination laws to its staff members, bolstering the impression that they were an abused population with many perquisites but few rights. The House had previously established procedures to combat bias against its own staff members.

Many arrive on Capitol Hill fresh from college, young but savvy, influential but with no real power, idealistic but adept at compromise. In the space of a couple of hours, they may be asked to draft a bill and fetch the boss's laundry, serve as political sounding board and chauffeur, negotiate a compromise and paint the boss's apartment. Their rewards are more psychic than financial. They lack job security, most earn $20,000 to $40,000 a year, and 12-hour work days are common.

Behind the Closed Doors

But some do wield impressive influence, mostly out of camera range, during closed-door negotiations. Just before the Senate passed a civil rights bill last Wednesday, Senator John C. Danforth, Republican of Missouri, rose to praise Dennis Shea, an aide who he said had negotiated a compromise with the White House, noting, "It was largely because of his efforts that we were able to put together the agreement."

Indeed, some members believe that aides have grown too powerful and their bosses too reliant on them. "I get so damned tired of members who can't go any place without staff," Senator Lloyd Bentsen, Democrat of Texas, said as he strolled across the leaf-strewn Capitol lawn recently. "They don't know the issues themselves."

In the Congressional hierarchy, committee staff members rate higher than a member's personal staff, perhaps because they become experts in subjects as diverse as arms control and wetlands. Many of them spend a few years on Capitol Hill before joining the bureaucracy, a downtown law firm or a trade association. A few eventually become politicians themselves, judges or regulators.

And some make it back to Capitol Hill. Three of the four Congressional leaders began their careers as aides: House Speaker Thomas S. Foley of Washington; Senator George J. Mitchell of Maine, the majority leader; and Representative Robert H. Michel of Illinois, the House minority leader.

Some reverse the process, a hint of one possible effect of the proposed limitations on the number of terms an elected official can serve. Floyd Fithian, a former Democratic Representative from Indiana who is now an aide to Senator Paul Simon, the Illinois Democrat, said the difference between the two jobs was that "there's much less running for the airport."

Most Congressional aides are in their 20's and 30's. Women outnumber men about three to one in policy jobs, which make up about 60 percent of those on Capitol Hill. Although women are in seats of power throughout Congress, men still occupy most of the top positions.

Members concede that they have come to rely more on their aides because the issues before Congress are more complex today. This is especially true in the Senate, where 100 members must keep up with the legislative issues handled by 435 House members.

Milton S. Gwirtzman, a lawyer who has studied Congressional staffing, says: "Their power is derivative, of course, but they have a wide range of discretion. Very often the matters are so complicated, and the pressures on the member of Congress are so great, that the member doesn't have time to consider an issue."

But Senator Daniel P. Moynihan contends that the legislative complexity is itself a byproduct of the large Congressional staff. "Things become complicated if there are enough people to complexify them," the New York Democrat said.

Each of the 535 lawmakers uses staff differently. Representative Thomas J. Downey, a Democrat who represents Long Island, said, "I use my staff both as a sounding board and to formulate and refine ideas."

Representative Ron Wyden, an Oregon Democrat, said, "For me, the single most important thing is the investigative role." And Representative David R. Obey, Democrat of Wisconsin, said, "I use staff to flesh out my ideas, to put the details on things I think are important."

Some members of Congress like their staffs lean. Representative William H. Natcher, a Kentucky Democrat who oversees billions of dollars as chairman of the Appropriations Subcommittee on Labor, Health and Human Services and Education, is parsimonious, with a personal staff of only eight. Their salaries range from about $16,000 to $33,000 a year. Mr. Natcher spends about $200,000 a year on his personal staff, less than half a member's allotment of $475,000.

On the Senate side, where expenditures are based on state population, Senator Alan Cranston, Democrat of California, spends more than $2 million a year on his personal staff.

Major Role on a Bill

Staff members can influence bills as well as merely write them. Gwen Gampel recalled that in 1987, as an aide to Representative Pete Stark, she played a major role in shaping the catastrophic health insurance bill. The California Democrat, as chairman of the Ways and Means Subcommittee on Health, had asked her to take the lead in writing the bill.

"I talked to everybody from academic types at Harvard to all the interest groups, and put together a bill for the Congressman," Ms. Gampel said. "Everything I put together on the benefits side he approved," she added, noting that it was adopted by Congress and signed by the President with but one major addition: a prescription drug benefit.

However, the bill created a furor among older Americans, who resented paying for the additional coverage, and Congress repealed it the following year. Ms. Gampel is now a lobbyist on health care issues. Giving Credit

Senator Moynihan attributes the success of his 1988 welfare reform bill to Ms. Burke, Mr. Dole's aide, who worked out an agreement on the workfare provision and said that "the key was to make it seem not onerous."

"There wouldn't be a bill without her," Mr. Moynihan said. "She took a subject about which her side of the aisle was anxious, and some things they didn't like got fixed, thanks to her."

"She can say to a senator: 'There's nothing in here any longer that would trouble you -- you can vote for this bill.' " Mr. Moynihan continued. "That's coinage on the Senate floor."

Senator Dole said, "Senators would rather talk to her than to me," adding, "She's in the middle of everything." Says Ms. Burke of her boss: 'I've never had him undercut me, and say, 'That's not a deal I'm going to buy.' "

Ms. Burke, the ultimate Congressional aide, has had her two children when Congress was not in session, and expects to have her third around Thanksgiving Day.

"I only have them during recesses," she said.