White collar federal workers would get a 6.9 percent raise in January under a long-shot (as in running a marathon in high heels) bill introduced yesterday by Rep. Stan Parris (R-Va.). All Parris has to do is convince about 400 of his colleagues that it would be a good idea.

Parris says that the increase, about double the amount President Reagan has proposed, is necessary to protect employes from a cut in take-home pay next year because of higher health insurance premiums, and a salary-cutting bookkeeping change that will be effective in January.

The Office of Personnel Management says that the 3.5 percent raise the president is offering is more than enough to offset the pay cuts--ranging from 80 cents to $8.80 every two weeks--and an increase in health insurance premiums, expected to average 19 percent, starting next year.

OPM says employes can avoid paying higher premiums by switching to less expensive policies during the open enrollment period. That open season starts Nov. 14.

The Parris pay plan isn't a shoo-in. Congress has tentatively approved a 4 percent federal pay raise for January, in the face of government pay data showing that white collar feds' salaries are 21.5 percent behind the going rate in private industry.

Among nonbelievers of the 21.5 percent pay gap are the White House and the OPM.

Administration officials say the survey doesn't reflect the reality of nonfederal pay scales, or salaries in state and local government. If the truth were known, the administration says, feds are lagging less than 4 percent behind their counterparts outside of government.

Parris said that most private sector wage settlements this year have been in the 6.5 to 8.5 percent range. In introducing the federal pay bill, Parris told colleagues that "after reductions are made in health benefits and the new pay formula is implemented, it will take at least a 6.9 percent pay increase to enable government workers just to break even."

A spokesman for the House Post Office-Civil Service Committee--which handles federal pay matters--said the committee did not know Parris was introducing the bill, "but we wish him well." An aide to Rep. Steny Hoyer (D-Md.) said he would "certainly support the idea" of a larger U.S. pay raise.

Washington area legislators are expected to back the higher pay raise.