Washington area blue collar federal workers have been getting substantially bigger percentage pay raises over the past six years than their white collar colleagues in government.

That same trend of bigger blue collar boosts tends to hold true for most workers in and around big cities like New York, Chicago, Seattle, Denver, Atlanta, Kansas City, St. Louis, Houston and on the West Coast.

Even with the higher percentage raises for government trades workers, craft employees and those in laboring occupations, their average salary here last year was $13,459 compared with an average of $17,961 last year for local white collar civil servants. Although that is still quite a pay gap, in favor of employees paid under the GS (general schedule system, the gap is slowly but surely closing.

First the dollar figures, then some of the reasons for them:

In 1969 white collar government workers got an average 9.1 per cent nationwide while blue collar government workers here received 6.7 per cent.

In 1970 the white collar increase was 7.5 per cent and there was no blue collar raise.

In 1971 the white collar employees went up 6 per cent while blue collar employees got 5.5 per cent.

In 1972 the white collar average was 5.5 per cent and the blue increase here was 5.7 per cent.

In 1973 the white collar raise was 4.8 per cent and the local blue collar raise was 6.8 per cent.

Blue collar employees got nearly double the 5.5 per cent white collar raise for 1974, averaging 10.2 per cent.

In 1975 blue collar workers here got 10.3 per cent for an average raise while white collar civil servants got 5 per cent.

In 1976 the white collar raise was 4.8 per cent and the local blue collar increase was 7.3 per cent.

Last October, white collar federal workers got a 7.05 per cent raise. The October increase for blue collar employees here averaged 8.52 per cent. Why?

There are a number of reasons:

Blue collar pay is linked to local prevailing industry rates; white collar federal pay is based on a national average.

The number of blue collar jobs, especially at the lower pay levels has decreased as government eliminates those jobs and/or contracts them out to industry.

The government can and does make adjustments for blue collar federal pay, raising rates based on private pay in other cities when there is no local private industry scale to compare it with.

In 1970 the average white collar federal employee here earned $12.832. Last year, before the pay raise, that average was $17,961. In 1970 the average blue collar federal worker here got $7,953. Last year it was up to $13,459.

Although blue collar federal workers still make much less on average than white collar employees, their pay here under the locally based wage system has almost doubled since 1970. White collar workers have not advanced as rapidly.

That data, which federal officials are studying now, could cut some of the arguments out from under unions that oppose an area wage type of system for white collar workers in clerical and administrative occupations.

That proposal - a rehash of a report made by former Vice President Nelson Rockefeller - is under consideration now by the Carter Administration. It would like government secretaries and support staff people to wages paid by local private firms for the same jobs, taking them out of the national average, across-the-board pay raise system.

Federal unions argue that abandoning the national average wage concept would mean lower future pay raises for white collar government employees living in smaller towns, and low cost geographic regions. But most federal employees now are concentrated in and around major metropolitan areas where wages based on local private industry have been going up faster - according to the government's own-data - than the national federal white collar pay raises.

Percentages are only useful, of course, when one asks the question percentage of what? Despite their "lower" average pay raises in recent years. White collar civil servants remain among the best-paid - if not the best paid - salaried workers in the nation. They still make a lot more than their blue collar federal counterparts. But it is food for thought, both for the Carter Administration and for the million-plus white collar employees who may, if Congress agrees, be going under an area wage type of systems within the next few years.