By the accepted rules of the game, Mike Ruddy has punched all the right tickets. He grew up in a middle class neighborhood, went to college, earned a master's degree, married, bought a house and carved out a career for himself.

But at 29 he has concluded that he "just can't live up to my middle class expectations.

"You always think you'll be better off than your parents, but these days you can't seem to do it," he says solemnly. "At times in the last few weeks, perhaps morbidly, I've been asking myself, maybe this is it, maybe things will never get any better."

Ruddy, a school teacher in suburban Prince George's County, is one of an increasing number of Washington area residents - especially those with families - who are finding they can't make ends meet on $15,000-a-year incomes, an amount most of them once considered a princely sum.

"If I knew at 20 that I'd be as broke as I am now, I would have been really depressed," he declares. "You just can't live on $13,000, $14,000 or $15,000 a year in this area if you have a family. I figure I'd need at least $17,000 to break even."

In a nation where the median family income is $13,720, the plight of Ruddy and others like him may not arouse much sympathy. By theirs is less a story of poverty than a commentary on the rising cost of the American dream, a dream that seems to recede no matter how much they earn.

The most disillusioned among them are public service workers: school teachers, policemen, firemen, low level bureaucrats and others like them. Their budgets have been thrown totally out of whack by a combination of inflation, astronomical housing cost, the area's high cost of living, easy credit, and, this winter, high fuel bills.

Some have sunk deeply in debt trying to live up to their expectations. Others have scaled down their vision of what to expect from life. "The old dream of a cottage with a white picket fence and two kids is almost gone for most of us," says Kenneth Roynestad, a Montgomery County policeman.

"When I got out of school the big thing was to make $10,000 or $12,000. I thought anyone making $15,000 would be living like a king" adds Douglas Ventura, another policeman, who earns $16,400 annually."But unless your wife works you can't make it in this area on a policeman's salary."

Mike Ruddy, his wife and fours sons live modestly in a two-thirds finished home they're building in Upper Marlboro. "I haven't been blowing my money," he insists. "I haven't bought any clothes for years. We don't have a color television. We hardly ever go out. Our car is 12 years old."

He expects to earn about $15,200 this year, $12,000 from his job as a teacher at Suitland Junior High School, and another $3,200 from a part-time real estate job. But this isn't nearly enough to pay his bills, he says."We're always strapped, very strapped."

In the last 18 months he has been caught in an incredible web of credit problems, most resulting from trying to build a new house for his growing family. He and his wife have been harassed by creditors at home and work. It has sometimes driven her to near tears. The only way they've survived is by borrowing from their parents, who, he estimates, have lent them $10,000 the last four years. "They've always helped us when we needed it, Ruddy says. "But it's really depressing to be so much on the ropes you have to ask for help."

It's easy to say, for example, that sending his two oldest children to private schools is extravagant (the monthly bill is $160). It's easy to say he could have spent last summer working at a paying job rather than in summer school, or that if he's interested in money he could have picked a higher paying career.

He admits as much. "A lot of my wouds have been self-inflicted," he said one afternoon in the teacher's lounge at his school. "You get yourself in a jam shotting for a dream."

His current dream is to finish a Ph. D. in educational technology, at the University of Maryland. He sees it as the light at the end of his financial tunnel. "I guess I see the Ph. D. as my ticket out," Rudy said. "When it's completed hopefully I'll get an offer to teach at some college and I'll be on the road to a career with both money and creativity.

There's good reason that $15,000 seems like less today that is was a few years ago. It simply is worth less. According to the Bureau of Labor Statistics, $15,000 today buys roughly half what it did 20 years ago, and only about two thirds what it did just six years ago.

The inflationary spiral has been especially dramatic in recent years. The purchasing power of $15,000 in 1970 shrank to $13,920 in 1972, $11,805 in 1974 and to just $10,230 in 1976.

Put another way, a $15,000 income in 1955 is comparable, in terms of what it could buy, to a $29,926 income today. A $15,000 income in 1960 bought what $27,640 would buy today,,$15,000 in 1970 bought what $20,602 would buy today.

Meanwhile , the standard of living has escalated dramatically, propelled upward by high government salaries and two-income families. According to the Washington Center for Metropolitan Studies, the area's median family income jumped from $7,464 in 1960 to $12,883 in 1970 to $16,900 in 1975. Although no firm statistics are available, experts estimate it has now risen to well above $18,000 areawide and perhaps as high as $23,000 in suburban Montgomery and Fairfax counties.

The things has hit hardest is the housing market. And the typical new home now sells for $58,000 in the area, the average older home for $66,900.

In some ways, Joe Scigliano, 26, is lucky. He has found a new town house for $42,500 in Gaithersburg which he is buying with no money down.

But he feels the house, with its $1,100 a year property tax bill, may be his undoing. "I'm selling everything I own to pay the closing cost," he said Monday. "A person on my salary with a family simply can't put together any savings. You have to live week by week."

He has taken loses on most of the deals. He sold his two prize shotguns, which he claims are worth $900, for $700. He sold his broken down MG midget for $250. He thought it would bring $450 to $500.

Scigliano, a father of two, earns $14,200 a year as a Montgomery County policeman. His part-time job as security guard brings in another $1,500 to $2,000.

His montly take home pay from the police department is $547. Of that, he now pays about $299 per rent, $160 to $180 for food, $15 for insurance, $25 on his Sears credit card bill, $70 for gasoline, and $25 for a phone. Without any expenditures for clothing, recreation or a host of other items, this adds up to $608 a month.

The real pinch will come when he moves into his new town house with his family in April. His monthly house payment and utility bills then will run about $500, leaving just $158 left over for all other expenses.

His part-time job will help some. But like all other Montgomery County policemen he is forbidden from working over 20 hours each week at a part-time job. He also picks up some extra money in GI bill benefits for taking college credits. "It may sound ridiculous, but I have to go to school to make ends meet," he explained. "I can't afford to live without those VA benefits."

Scigliano sees no easing of his financial plight in the foreseeable future. "It's a part of life," he said. "It's just the way things are going to be for me for a long time unitl someone gives us a big raise."

He paused, then added philosphically: "The funny thing is that $14,000 or $15,000-a-year sounds like a lot of money. But it's just no any more.I'd say you'd need at least $20,000 a year to live without begging, borrowing or stealing."

You might say P.J. arschner lives the good life. She good life. She sails, plays tennis lives in a comfortable neighborhood in Northwest Washington, flies home to Florida five or six times a year, goes out six or seven nights a weeks, and the nights she doesn't go out she and her two roommates more often than not have someone over for dinner.

She also makes about the same amount of money as Mike Ruddy and Joe Seigliano. The difference is she is single. It also is helpful that she is a very attractive young woman. "About half the time that I go out someone else picks up the tab," she said sheepishly the other day in her office off DuPont Circle.

THis obviously bothers her. "Working for a feminist organization that isn't the kind of thing you like to have spread around," she said.

Marschner, 26, works for the Center for Women Policy Studes. Last year, she earned about $14,000. This year she expects to increase that a couple thousand dollar by teaching part time.

This shocks her friends back home in St. Petersburg, Fla. "Down there, you say $14,000 or $15,000, and they say, 'All that money. You must have money to burn.'"

"Money is different here" she added. "People make a lot more money here that they do in most place in the country."

P.J. Marschner doesn't have money to burn, although she say, "I think I do very well on what I make." A glimpse of her montlhy budget shows why her financial situation is so different from that of the Ruddy of Scigliano families.

The big difference is housing and food. She pays only $185 a month rent for the large house she shares with two other women in Spring Valley neighborhood of Northwest Washington, no more that $100 on food, and often less. She puts about $200 away in saving, pays $30 for old student loans, an average of $100 a month for tuiton in the Ph. D. program she is taking, an average of $100 for air fare and $100 for auto expenses. The remainder of her take home pay is eaten up by credit card bills of one sort or another, and entertainment.

She's careful about money. She shops for bargains, and has learned to take advantage of the free recreation opportunities the city has to offer.

"I've thought about it, and I don't see how families make it on $15,000," he she said.