The 4.8 percent pay raise President Reagan is proposing this October would be the smallest increase U.S. white-collar federal workers have received since the middle of Lyndon Johnson's administration, when they got a 2.9 percent increase in 1966. And it is peanuts compared with the "salad days" of the Nixon years, when federal pay jumped nearly 50 percent.

Federal workers this year may be "lucky" if they get the Reagan raise. Key members of Congress, in both parties, have asked the White House to shave the 1981 pay raise a little closer.

Jimmy Carter's final budget projected a 5.5 percent civilian increase. Reagan's revised budget lowered the target figure to 4.8 percent, based on the assumption that Congress will approve his federal pay "reform" bill to change the way government salaries are compared with private-sector pay.

Until passage of the so-called Federal Comparability Pay Act, federal pay raises were handled by Congress.There was no such thing as a regular guaranteed raise. In 1945, federal workers got a wartime catch-up raise of almost 16 percent. The next year, they got another 14 percent increase.

In 1948 white-collar federal workers got an 11 percent raise. The next year they got 4 percent and, in mid-1951, another 10 percent increase. It was four more years before civil servants got their next raise, a 7.5 percent increase. In 1958, they got 10 percent and, in mid-1960, 7.5 percent.

The pay raise under President Kennedy came on October 1962: 5.5 percent. During the Johnson administration federal white-collar workers got two raises, of 4 percent and 4.2 percent, in 1964, a 3.6-percent raise in 1965, 2.9 percent in 1966, 4.5 percent in 1967 and 4.9 percent in July 1968. Federal pay jumped more than 40 percent (excluding compounding) during the Nixon years, when the so-called comparability-with-industry law was passed by Congress. There was a 9.1 percent increase in July 1969 and another 6 percent raise in December of that year. Jan. 1, 1971, brought a 6 percent raise, followed in 1972 by two more raises, of 5.5 percent and 5.1 percent. There was a 4.8 percent raise in October 1973 and, in 1974, a 5.5 percent raise (authorized by Nixon but implemented by Gerald Ford).

President Ford gave federal workers a 5 percent raise in October 1975 and 5.2 percent in October 1976, one month before he lost a squeaker election to Jimmy Carter.

Carter's first pay raise for federal workers was a 7.05 percent adjustment in October 1977. He authorized a 5.5 percent raise the next year (about half the industry pay raise, according to federal pay experts) and 7 percent in 1979. That was the biggest increase in some time, but federal unions complained it should have been double that amount to keep up with industry. Carter proposed a 5.5 percent raise for federal workers for 1980 but changed it just before the election to 9.1 percent.

Federal pay raises are sometimes called cost-of-living raises. They are not.The increases are based on surveys of private-sector wage gains (made by the Bureau of Labor Statistics). The president and his agents then determine what amount is needed to bring U.S. pay up to industry levels. If the president decides to lower the amount of the October raise, he sends an alternate plan to Congress in late August. That alternate plan, with the lower amount, automatically goes into effect in October unless Congress vetoes it and demands a higher U.S. pay raise. It doesn't usually do that.

Reagan says there will be no need for an alternate pay plan this year if Congress approves changes he (and Carter) proposed in the way government compares its compensation package with industry. The Reagan proposal would tie U.S. salaries to local industry levels, peg the so-called "comparability" figure at 94 percent of industry pay and match the value of Uncle Sam's attractive fringe benefit package against industry wages and benefits. With those changes, the Reagan people say, the raise this year will work out to about 4.8 percent. But some members of Congress are talking about separate legislation to lower the federal pay raise this year or to kill it altogether.