The 300,000 white-collar federal employes in the Washington area would get a 6.2 percent pay raise this October under President Carter's new budget -- short of the 10.9 percent raise that is estimated as being needed to bring them up to the salary level of private employes.

Military personnel, who in the past usually have gotten the same raise as federal civilian employes, would get a 7.4 percent raise this fall, under the budget Carter submitted to Congress yesterday.

Carter's pay proposals assume that Congress will pass his controversial federal pay reform package before it recesses this summer. The bill would change the method the government uses to set its salaries in comparison with the private sector and separate civilian and military pay rates.

Even if the bill is not passed, the president still could recommend that federal employes get less than a 10.9 percent raise -- as he has done for the past two years. That recommendation is due by August.

Under the pay reform proposal, the government would match the value of employe fringe benefits -- vacations, holidays and retirement -- against those offered workers in similar jobs in the private sector. Federal officials estimate that such comparisons would reduce future federal pay raises. The change proposed for this October, based on passage of pay reform, similarly would trim the anticipated "comparability with industry" raise from 10.9 percent, to 6.2 percent proposed in the budget.

The federal payroll dominates metro Washington's economic picture. The monthly civilian white collar payroll exceeds $700 million, and that figure balloons when salaries for postal workers, 60,000 local military personnel and the pensions of 100,000 civilian and military retirees are included.

The straight "comparability" pay increase of 10.9 percent would boost the federal payroll here about $76 million a month. Under Carter's proposal, though, that amount would be cut to $45 million monthly.

Passage of pay reform is doubtful. There is strong opposition in Congress, especially from the South. Under the plan, federal wages around the country would be tied to salaries paid in local industries. That probably would mean smaller raises for civil servants in many rural regions where military installations are located.

White House sources said yesterday that President Carter still could reduce the amount of the October raise even if Congress fails to approve the reform bill then.

For the past two years, Carter has trimmed the raises that would have brought civil servants up to the level of private industry. In 1978, government data showed that employes were due an 8.4 percent raise. Carter, with congressional approval, limited the raise to 5.5 percent. Last year, white-collar employes got a 7 percent raise, down from the 10.4 percent level that would have brought them into line with the private sector.