Despite attempts to freeze the federal payroll next year, about 40 percent of the government's 1.4 million white-collar civil servants will get 3 percent salary increases in 1986.

The statutory raises, guaranteed by law, are based on time in grade and satisfactory service.

The increases are not affected by the 1986 pay freeze called for in the budget approved earlier this summer by the Senate and House. The Senate originally had proposed delaying the longevity raises for a year, a plan that was rejected by the conferees.

Most white-collar workers get longevity raises (in addition to any general pay increase) every one, two or three years. Those increases are based on a performance rating of "satisfactory" and their time in the grade.

Currently about 99 percent of all employes normally get the raises.

Each of the 15 primary civil service grades (GS 1 through GS 15) have 10 seniority pay steps. The salary differential from the bottom to the top of each grade is about 30 percent.

If an employe remained in the same grade, it would take 18 years to move from the first pay step to the top of the grade via the longevity route.

Here are two examples of the pay spread: GS 12, the most heavily populated grade here, has a starting salary of $31,619 a year and a top salary of $41,105. GS 7, the next most popular grade, ranges from $17,824 to $23,170 a year.

Nonsupervisory employes with satisfactory job ratings are eligible for a step increase every 52 weeks in steps two, three and four.

They must have been "in grade" 104 weeks and have a satisfactory job rating to be moved up to steps five, six and seven. They must wait 156 weeks to be advanced to steps eight, nine and 10.