Sharon Smith might win a popularity contest elsewhere in America, but she doesn't stand a chance in the nation's capital.

"I want to be fair to government workers but also to the taxpayers," says Smith, a 29-year-old economist who spent several years studying the relationship between salaries paid government workers and those paid employees in the private sector. Her finding: most federal employees are paid between 13 and 20 percent more than they would be if Uncle Sam didn't sign their paychecks. And that doesn't take into consideration benefits, such as vacations and pensions, that sweeten a civil servant's lot in life.

A book Smith wrote on her findings, published late last year by Princeton University, was first passed around the Washington bureaucracy by a government economist. And now Smith's work has become a subject of interest among those who must decide the delicate issue of federal salary levels.

Titled Equal Pay in the Public Sector: Fact or Fantasy, Smith's academic but lucid study took a dramatically different approach to determining levels of compensation.

While federal pay experts set pay scales by comparing jobs in private industry with similar government jobs, Smith took another view. Under a grant received by Albert Rees - first director of the Council on Wage and Price Stability and a Princeton professor - Smith compared workers instead of jobs. Instead of comparing, say a secretary in a corporation to a secretary at HEW, she considered the age, sex, educational background, geographic location and other factors of the two secretaries. Then she compared their wages. Her findings confirmed the belief of every hardhearted taxpayer who thinks public servants live too highly on his tax dollar.

"I'll concede that some upper-level people are underpaid," says Smith, who now works as a researcher for the Federal Reserve Bank of New York. (She graduated Phi Beta Kappa, first in her class from Rutgers, then earned her Ph.D. in economics there.) "But the professional, managerial types may be getting something in non-wage compensation. For example, what did being Secretary of State do to the market value of Henry Kissinger's memoirs? But, yes, some government executives could earn more money in private industry. It's the lower level workers who make out the best."

Other benefits Smith points out: stability of employment, handsome vacation allowances, pension plans often tied to the cost of living, and "the opportunity to do a job they wouldn't get to do in the private sector - though after they've done it, they may be able to move into the private sector."

Smith notes that if federal wage levels were unattractive, the government would experience a shortage of job applicants; quite the contrary is the case, which lends weight to the argument that wage increases are unnecessary in the near future.

Smith has communicated with the Office of Management and Budget (after she wrote President Carter last October recommending he forgo the five percent salary increase for federal workers), and a House subcommittee considering postal workers' wages requested her study. But she feels some frustration at the low-profile nature of what she calls "an exceptionally good piece of research." And she notes the irony: from start to finish, her work was financed by federal funds.