When people explain why they support President Carter's proposals for curtailing veterass' special advantages in federal employment, they often cite illustrations such as these:

A 50-year-old black woman has been doing laundry for the Air Force for 12 years and has no other skill. Officials say they have to fire her to make room for a male veteran whose firefighter job at Eglin Air Force Base (Fla.) is being abolished, and whose rights as a veteran allow him to take her job."

A woman took a federal civil service exam for a post in Dallas as an air controller and scored a per-plicants tied for first place. After fect 100, becoming one of seven ap-the extra points given to veterans were figured into the scores, the woman had sunk to 147th place."

An unemployed Vietnam vet must compete for a government job with a Korean War veteran who already has one and yet still gets the same extra points as the younger man."

Such cases are not rare, but typical of the preference law's impact on the "have-nots" in the work force, according to the advocates of change.

Arrayed against them, however, is the proven might of the veterans' lobby and its supporters in Congress. They oppose any changes in their lifelong preferences.

The veterans won round one in the congressional arena last week when a Senate committee voted to toss out the veterans preference changes which Carter had called for in his civil service revision bill. Administration officials have vowed to continue fighting for alterations though they have also said they are willing to compromise on the degree of change.

Carter has proposed to "refocus" the veterans job preferences, cutting them back for older able-bodied veterans (the majority) and maintaining or increasing them for disabled and Vietnam era veterans.

But spokesmen for veterans groups argue that veterans earned job preference as part of a good-faith deal they cut with the government in exchange for their service.

They maintain also that veterans are getting blamed unfairly for the government's own "systemic" failures in affirmative action programs.

Backers of the changes insist that the intent of the Veterans Preference Act of 1944 was to ease the transition to civilian life for returning veterans by giving them an edge in getting and holding jobs during that period, not to reward them with "an edge forever."

Veterans now hold half the jobs in the federal government, although they make up only about one-fourth of the nation's total work force, according to the Bureau of Labor Statistics.

Frustrated federal managers complain that because of their lifelong preference rights, older veterans "choke the pipeline" of job applicants, preventing the hiring of young veterans, or nonveterans who may be better qualified, and that in the event of a layoff, veterans must be the last to go.

"We really worked out tails off to recruit well-qualified women and blacks to apply for positions, but we can't get them to (the top of the hiring lists) where we can pick them because fo veterans preference," said Donna E. Shalala, a deputy assistant secretary of the Department of Housing and Urban Development.

The almost 30 million veterans in the country are 98 percent male and 92 percent white, government figures show.

Male veterans hold around 65 percent of government supergrade jobs, while women hold 3 percent, according to the Veterans Administration (VA).

And, Shalala pointed out, it is often the older veterans who show up at the top of the lists she must hire from, men "already in the government, trying for a better job."

Roughly 45 percent of the veterans hired last year by the government had completed service before 1965, government figures show.

The revisions proposed by Carter acknowledge that veterans deserve some special breaks, but would direct the advantages to "those veterans most in need of assistance," according to Civil Service Commission Chairman Alan K. Campbell, who has been pushing hard for the changes.

For most able-bodied veterans, the original Carter plan would put a 10-year limit on the federal employment advantages. (Under a more recent compromise plan that limit would be raised to 5 years, or a one-time sucessful use, whichever came first, in order to benefit more Vietnam veterans.)

Carter would also eliminate the extra exam points given high-ranking retired officers when they seek government jobs and become so-called double dippers.

At last count, almost 28,000 retired officers were collecting military pensions while working for the government, according to a 1976 congressional study. (There were about 112,000 retired enlisted personnel working for the government while collecting military pensions. Along with the officers, they make up about 5 percent of the civilian federal work force.)

The changes the president proposes are essential in order to eliminate some of the "rigidities and unfairness" in the present civil service system, and to put "merit back in the merit system," Campbell says.

"Veterans preference is itself a form of affirmative action. The question is whether other groups should also get that kind of affirmative action."

However, Campbell and other supporters of the changes say that, even if they are enacted, they will have little impact on the broader problems of employment for minorities and women. The government is filling only about 150,000 new civil service jobs each year, and layoffs affect only 7,000 to 10,000 federal employes annually.

The political climate around veterans has been changing, according to Leslie Gladstone, a lobbyist for the Women's Equity Action League, one of several women's groups working for changes in veterans preferences. "It isn't 1944 anymore," she said.

Nationwide, at the state and local level, several jurisdictions already have curtailed veterans preference provisions, or are in the process of doing so.

And a growing number of members of Congress feel that, as one put it, "there is at least some middle ground to be explored" on the issue.

But the veterans' bottom-line argument is their raw political clout in Congress. As American Legion lobbyist Ed Lord put it, "In an election year, nobody is going to vote against veterans preferences."

The often passionate reaction by veterans' groups against Carter's proposed changes is just part of a broader "cumulative" reaction against a whole series of Carter initiatives, their spokesmen maintain. Last fall, the new national commander of the Veterans of Foreign Wars was quoted as calling Carter's administration "the most antiveteran" in the nation's history.

Lord characterized the nation's veterans as a "sleeping giant" being aroused to anger by administration moves such as the "pardons for draft dodgers," and efforts to tamper with veterans' education and hospital programs, which they view as part of the spectrum of special rights they have earned.