A report due this week is expected to say that 100,000 or more white collar U.S. workers are being overpaid for the jobs they do.

That represents a lot of people - nearly one worker in every 12 - and millions of unnecessary dollars paid for inflated salaries. It is a lot lower than the government estimate of last April, which said there were 150,000 employes being paid too much because their jobs were overgraded.

The original estimate, taken from a Civil Service Commission study, said $280 million was being wasted each year paying employes more than their worth. It was based on a small but "statistically good" survey of less than 1 percent of the government's white collar jobs. Now that study is being revised. Insiders say the estimate of the overgraded jobs will be cut by about one-third, thanks to new and better data.

The earlier CSC study was pulled back before it could be released, but not before Commission officials had announced premilinary findings to professional groups and data was widely reported in the press. The original study, which has been corrected, also showed that about 45,000 workers in Grades 1 through 15 were graded too low, and therefore making less than they should.

Last week the American Federation of Government Employes attacked CSC for publicizing the data, and challenged it to release the report. The union was tipped off from inside the Commission that the study had been revised.

Even the new, improved study is likely to have its critics, since it represents only about a 1 percent sampling of the federal work force. But whether the number of overgraded is 100,000 or 150,000, it certainly will speed agency downgrading actions in the months ahead.

Underground Man: General Services Administration chief Jay Solomon went underground last week. But it had nothing to do with the on-going investigations of corruption he inherited in the house-keeping agency. Rather, it was to investigate complaints from GSA workers who man underground steam tunnels that honey-comb Washington.

Few GSA brass have even been in the hot-air catacombs. Most people do not even know they exist. However, Solomon and the head of GSA's region 3 here decided to take a first-hand look to see, and feel, working conditions. "It was as close to hell as I ever hope to be," one member of the party said of the trip. As a result of their first hand steaming, word has it some work on environment improvements is on the way for the people who keep the bureaucracies radiators going.

Political Endorsements; Eighteen major federal and postal unions, both independents and AFL-CIO, have endorsed Reps. Gladys N. Spellman (D-Md.) and Herbert Harris for reelection. Most of the groups have also endorsed Rep. Joseph Fisher (D-Md.) but some AFL-CIO affiliates have declined because Fisher is not 100 percent behind their plan to modify the Hatch "no politics" Act.

Chief Postal Inspector C. Neil Benson has received the top leadership award of the Association of Federal Investigators. The Postal Inspection Service is the nation's oldest investigative arm (according to the Service) and has a conviction rate higher than any other federal law enforcement agency.

That Was No Penguin! Alan Whitney, vice president of the National Association of Government Employes union had an unexpected caller Friday. His staff ushered in a young man wearing white tie, tails and a top hat. Ever the optimist, Whitney hoped the National Symphony Orchestra had come to sign up. Instead, the young man began to warble a happy birthday greeting.

Whitney suspects his wife and daughter financed the singing telegram. His age was not disclosed. But informed sources say Whitney will see 39 again.

Restoring Credibility in Public Institutions: Sounds like a tall order, but the prestigious American Association for Budget and Program Analysis will make a stab at it Nov. 6 and 7. Their symposium, at George Washington University, features top U.S. officials. They will talk about the taxpayer revolt, job freezes and new budget techniques.

Price for the sessions (agencies can pay for this) is $50 for members, $65 for others. Writer the AABPA at P.O. Box 1157, Falls Church, Va., 22041.

Four Star Production: American Society for Public Administration has one set for its Nov. 30-Dec. 1 Capital Hilton Hotel conference. Keynoters for the session on "The Dynamics of the Federal System" are Jean Houston, President of the Association for Humanistic Psychology; Pulitzer-prize winning columnist (The Washington Post) David Broder; Mayor-apparent Marion Barry, and pollster Louis Harris. Call George Bickerton at 301-436-8051.