Judy Ives has heard all the excuses. That men's work is worth more than women's work. That men need money to support families. That she should be happy to have a job and shouldn't rock the boat.

"But I still don't see what it is about a tree-trimmer's job that makes it worth more than an intensive-care nurse," says Ives, 39, one of eight nurses who last year brought a sex-discrimination suit against the city and county of Denver for paying its tree trimmers, painters and tire-service men more than its nurses.

A registered nurse with more than 15 years' experience, Ives said she "was shocked at the inequities" in Denver's pay scale. Starting salary for its predominantly female staff nurses is $1,064 a month while beginning pay for its predominantly male tree trimmers is $1,164 and for painters, $1,191.

"It's not that, I think tree trimmers should receive less," adds Ives, who recently quit her job to return to school for her master's degree. "But I worked with critically ill patients in surgical intensive care -- probably the most intense unit in the hospital.

"Often that means working seven days straight, working holidays and nights and many times not even breaking for lunch. Patients are on life-support systems and need constant care. With that kind of responsibility I feel we should be receiving comparable pay."

The "Denver eight" lost their case in U.S. District Court last year, when the judge ruled that their claim was Pregnant with the possibility of disrupting the entire economic system of the United States."

The nurses are appealing the verdict. But the question they raised has become what some call the hottest new issue for working women -- the practice of paying men in male-dominated jobs more than women in female-dominated jobs.

With the rallying cry "equal pay for work of equal value," women are questioning the system that pays painters more than nurses, liquor store clerks more than teachers and truck drivers more than secretaries.

Ives' situation is not uncommon. While the Equal Pay Act prohibits wage discrimination on the basis of sex when a man and women do the same job, it's not so clear-cut when the jobs are different.

What is the worth of different kinds of human labor? In our society, which frequently measures worth in dollars, consider some examples:

In Montgomery County a liquor clerk 2, with a high-school diploma and two years of experience, earns $12,479 a year. A county school teacher with a bachelor's degree and two years of experience receives $12,323 a year. More than two-thirds of the county's school teachers are female and nearly all of its liquor clerks are male.

The University of Washington in Seattle pays its secretaries with two years' experience between $847 and $1,085 a month. The college truck drivers receive a starting salary of $1,168 to $1,289.

The median pay for full-time women workers in the U.S. is $8,618 a year, and for full-time men workers, $14,626 year, according to the U.S. Departments of Labor and Commerce. Although women earned nearly 64 cents for every dollar earned by men in 1955, today they earn just 59 cents for every dollar that men earn.

This wage gap is widening because "the majority of women work in 'women's jobs' that are undervalued and underpaid," said Equal Employment Opportunity Commission chair Eleanor Holmes Norton at a recent D.C. conference on pay equity.

"I think it's important to come to grips with the hard reality that women's jobs will remain a pattern of work for women in years to come, despite all of us going to law school, medical school and getting our Mba''s," said Norton, adding that only 6 percent of craft workers and 23 percent of managers and administrators are women.

The practice of paying women less than men for jobs that require comparable skill, responsibility and effort is Comparable to the separate-but-equal laws that used to apply to blacks," said Norton, who urges fighting the practice -- discriminantly -- in the courts. "It is hard to believe that female jobs are inherently worth less."

"Comparable worth," she claims, will be the most important issue of the 1980s for the average woman. "The trouble is," Norton acknowledges, "the average woman hasn't heard of it."

Stressing that "enlightened leadership" is necessary to achieve equal pay for work of comparable worth, Norton said the EEOC is working on the "establishment of valid job evaluations that take into account all relevant job factors and are free of bias."

Besides drawing up guidelines for fair job evaluations, EEOC also has commissioned the National Academy of Sciences to study whether objective, bias-free job evaluations exist or can be developed. That report is due in December, after which the commission plans to hold public hearings on the issue.

David Thomsen, director of the Compensation Insitiute in California, says organizations use two basic types of job evaluations:

One that looks at external factors and determines pay by what the job is paid in the marketplace. This method tends to reinforce traditional inequities.

The point-factor approach, which looks at characteristics found in a position -- like skill, responsibility and effort -- and compares it with other jobs in the organization."

While the most equitable job evaluations use point factors, Thomsen says that method can still perpetuate discrimination by defining characteristics that reflect a bias towards a particular group, or by using different pay scales for men's and women's jobs.

The University of Washington, for example, assigns 93 points to food-service workers, most of whom are female, and pays a starting salary of $646 to $827. Traffic guides, most of whom are male and whose job is to sit in a small structure at the edge of campus and issue passes to cars, are assigned a lower figure, 89 points, and receive a starting salary of $806 to $1,032.

While Thomsen says some companys' "new vice president of human resources take an advocacy role in comparable worth," other organizations are opposed to the EEOC's efforts.

The idea of structuring salary according to a "non-biased job evaluation," rather than by the wage offered in the marketplace, will most likely mean added payroll expenses for employers.

A recent article in Fortune magazine calls equal pay for work of equal value a "fallacious notion that apples are equal to oranges and that prices for both should be the same, even if that means overriding the law of supply and demand.

"The EEOC efforts, if successful, could upset myriad, long-accepted business practices," says the article. "It could have an enormous inflationary effect.

"At the extreme, to raise the aggregate pay of the country's 27.3 million full-time working women high enough . . . would add a staggering $150 billion a year to civilian payrolls. Such a radical step, of course, seems too preposterous to be taken seriously."

Holmes' rebuttal: "The economic issue is used as a scare tactic. I can't imagine that we would effect a remedy that all at once would change the wage system." Rather, she says, the impact would probably be gradual.

"Employers should look at their job-evaluation guidelines," she cautions, "before the EEOC guidelines come out."

She cites a conciliation agreement the agency signed with General Electric last year, in which GE agreed to boost pay for some underpaid jobs, most of which were held by women. The 1978 Civil Service Reform Act's provision that "equal pay should be provided for work of equal value" Norton sees as a reflection of increased federal interest in the issue.

Some activists see as a possible boost for comparable pay a recent U.S. District Court ruling that the Government Printing Office has been guilty of discriminating against more than 300 women employes because of their sex.

Spearheaded by Dorothy Thompson, a 58-year-old grandmother who has worked in book binderies for 33 years, the female plaintiffs charged that their work on the complicated bindery sewing machines is substantially similar to their male colleagues' work on the cutting and gathering machines. But they are paid about $4 less an hour than the men.

Citing evidence that both groups of workers perform jobs of practically equal difficulty, Judge Charles R. Richey ruled that the GPO's separate classification system for male and female workers "operates to perpetuate the effects of past discrimination and is not justified for business purposes or any other reasons." He has not yet determined appropriate action in light of his ruling.

While the bindery jobs are obviously more similar than jobs such as secretaries-truck drivers, D.yc. attorney for the plaintiffs Nora Bailey sees the case as haveing "potentially broad ramifications" for the issue of comparable worth.

"No men operated the large sewing machines, and no women were permitted to operate the cutters and gatherers," notes Bailey. "The only job held by women was outside the male classification system."

Says Thompson: "For years they told me the big industrial sewing machine I operate was women's work. But I knew all along I was doing a job same as men, but not getting paid the same."

Defenders and critics agree that it's a complex, subtle issue, steeped in tradition and surrounded by subjectivity.

"The roots are deep," concedes Eve Johnson, coordinator of women's activities for the American Federation of State, County and Municipal Employes.

"This summer my son mowed lawns for $6 a lawn. The average lawn took an hour to now -- he did pay for gas -- but he made nearly $6 an hour and spent afternoons at the beach.

"My daughter got up a 6 a.m. to babysit -- make breakfast clean the kitchen, feed the kids lunch, take them to Little Leauge, put them in their pajamas. She got less than $2 an hour.

"Most people would consider their kids more important than their lawn. But at age 13 my daughter understood her value in the marketplace in relation to her brother." CAPTION: Picture 1, $12,479/year Liquor store clerk in Montgomery County, high-school degree and two years' experience; Picture 2, $12,323/year School teacher in Montgomery County, bachelor's degree and two years' experience; Picture 3, $1,191/mo. Salary for painters in the City and County of Denver, Colo.; Picture 4, $1,064/mo. Salary for registered nurses in Denver; (KEY OFF) icture (KEYWORD) 5, $1,168-$1,289/mo. Starting salary for University of Washington truck drivers, like David Barnum; Picture 6, $847-$1,085/mo. Salary for University of Washington secretaries with two years' experience, like Gail Latham; Picture 7, $11.94 per hour The minimum for GPO journeyman bookbinders like Earl Rosemond; Picture 8, $8.11 per hour A typical wage for GPO bindery workers such as Dorothy Thompson