President Reagan has recommended to Congress that federal white-collar workers receive a 4 percent pay raise in October instead of the 18.47 percent increase that a study found would be required to match comparable pay levels in the private sector.

The 4 percent increase, which will take effect the first full pay period in October unless Congress intervenes, would go to about 1.4 million federal workers, administration officials said.

The pay recommendation was immediately assailed by the American Federation of Government Employes, which represents 700,000 federal workers, as failing to keep pace with inflation.

"We don't like it worth a damn," said George Hobt, director of pay and classification for the union. He said the proposed 4 percent raise would be wiped out by inflation running 7 to 8 percent a year and by the 1.3 percent Medicare tax to be withheld from federal employes' paychecks. "Federal employes are falling behind," he said.

The president's recommendation was released Thursday in Santa Barbara, Calif., where he is vacationing.

Federal law requires that government salaries be approximately comparable with those for similar jobs in the private sector, although presidents often have recommended less for federal workers.

The Federal Pay Comparability Act of 1970 also requires an annual survey to determine what adjustment would be necessary to bring federal workers' salaries in line with what the private sector pays.

After the survey, the president's "pay agents"--currently Labor Secretary Raymond J. Donovan, Office of Management and Budget Director David A. Stockman and Office of Personnel Management Director Donald Devine--suggest a pay level for federal white-collar workers.

This year, the survey found that an 18.47 percent raise would be required to keep federal white-collar employes at the level of workers in the private sector.

The "pay agent" forwarded that recommendation to Reagan.

Following the pattern of previous administrations, Reagan decided not to follow the panel's recommendations, citing "economic conditions."

In his fiscal 1983 budget submitted to Congress last February, Reagan asked for a 5 percent raise for federal white-collar workers; Congress later wrote a 4 percent increase into the budget reconciliation bill, and Reagan made his recommendation in line with that.

OMB calculates that each percentage-point increase in federal white- and blue-collar pay boosts federal budget outlays by $500 million.

The president's suggested 4 percent pay increase will go into effect in October unless Congress overrides it, which is not considered likely.

The increase would put pay levels for officials in the Senior Executive Service in the $56,945-to-$67,200 range.

However, there is a congressionally mandated ceiling of $58,500 for these top-level employes, according to OPM.

Pay levels for the General Schedule employes would range from $8,676 (GS-1 level) to $78,184 (GS-18), but the congressionally mandated pay ceiling for this group is $57,500.

By law, military pay increases parallel those for federal white-collar workers. Reagan noted in his statement that if Congress passes legislation to increase military pay more than the 4 percent he is recommending, the higher amount would stand.

However, Congress is not expected to recommend more than a 4 percent increase for the military.

The Senate Armed Services Committee is expected next month to recommend a 4 percent raise for the military, except for new recruits, staff aides said.

The House Armed Services Committee has approved legislation leaving military pay increases up to the president.