The Congressional Budget Office says Uncle Sam's pay and fringe benefits have slipped so far behind the private sector that the government would have to give its million-plus white-collar workers a 20 percent pay raise this year to bring total compensation in line with industry.

CBO's report--which is certain to raise some eyebrows in the private sector--was prepared for the House Post Office-Civil Service Committee. The report says that the federal retirement program is generally much better than anything industry offers its workers. But in other areas--like vacation, sick leave and health insurance--the CBO study says that the government is lagging behind progressive firms.

CBO's assumptions are based on actual 1980 data and on estimates for 1983 of the value of fringe benefits as a percentage of payroll. Firms surveyed are those that the government uses to make its annual study to determine how much of a pay raise civil servants are due in order to make their salaries "comparable" with industry's.

Reagan administration officials (and Carter administration officials before) argue that the system used by government to measure pay is skewed in favor of federal employes because it does not include wages and benefits of the 12 million state and local government workers.

Chairman William Ford (D-Mich.) of the profederal worker PO-CS Committee feels the report "shatters the popular misconception" that federal pay and fringe benefits are far better than those in industry. Ford, who favors a minimum 4 percent federal pay raise this year, said the report shows that this administration "clearly is guilty of distorting facts and figures" in an attempt to "mislead the public" into supporting federal pay freezes and assaults on the U.S. retirement program.

Ford said the report shows that federal workers put in longer hours, and have less generous health and life insurance benefits, less vacation, fewer holidays and less sick leave than employes have in the firms surveyed. A Reagan administration official said yesterday that the survey findings are "not particularly valid" because the majority of American workers do not get the kind of pay and fringe benefits provided by the firms in the survey.