Government engineers, medical personnel, scientists and Washington-based secretaries and clerk-stenos could get substantial raises if Congress and the White House go along with a pay bill drafted by Sen. John Glenn (D-Ohio).

The proposal, part of an overall pay package for all government workers, could have a long-range impact on the paychecks of workers in less competitive federal jobs or who are in areas where the job market is tough, or living costs are low.

Glenn's bill cleared his Governmental Affairs Committee last week. It would give agencies authority to pay differentials of up to 60 percent to the 200,000 workers who get special rates because they are in hard-to-fill jobs. Currently, they get salaries ranging from 2 percent to nearly 30 percent above the scale for their grade.

The government started the special rate program in 1955. At that time, it was mostly to help agencies get and keep engineers. But as private sector pay moved ahead of federal salaries in many occupations, the government expanded the special rate authority. Today, engineers make up about half the special raters. Many medical and scientific personnel have been moved into the special rate category, as have professional and technical people in cities such as New York, Los Angeles and San Francisco. More than 30,000 clerical workers in Grade 2 through 7 jobs in the Washington area are now in the special rate category.

Glenn's bill is attractive to budget watchers. It would let agencies selectively target those jobs in areas where they are behind private industry. It would also take some of the pressure off the government to attempt to solve pay problems in some areas and occupations by giving across-the-board raises to all workers.

The House has its own federal pay plan, as does the White House. Officials hope to reach a compromise next month. Waiting for Back Pay

Meanwhile, special rate employees are still waiting for the Office of Personnel Management to come up with court-ordered "conversion rules" that will decide which special raters are due money for parts of general pay increases that were denied them during the early 1980s. The OPM has been working on the rules -- a complex, nightmarish chore assigned by the court -- since March 1989. It grew out of a lawsuit brought by the National Treasury Employees Union. Although employees won most of the rounds, they have yet to see any of the money. Vacation Planning

Thousands of federal workers, journalists, lobbyists, lawyers and association employees have to plan their vacations around the congressional schedule. If you are waiting for word on when to head for the hills or beach or tackle the grass on your lawn, here is the tentative congressional schedule:

Both the Senate and House have tentatively scheduled the August-Labor Day recess to run from Aug. 6 to Sept. 4. The House will be out Sept. 20 for Rosh Hashanah and Sept. 29 for Yom Kippur. The Senate and House hope to adjourn Oct. 5.