Charles and Mary Mochwart partook of the finer things of life: a $600,000 house in Montgomery County, a Mercedes-Benz, domestic help, private schools for the children, and membership in two country clubs.

But after being married more than 20 years, the Mochwarts found themselves in divorce court, and when they appeared at a hearing to set temporary support payments, it was another aspect of their life style that caught the attention of D.C. Superior Court Judge Frank E. Schwelb.

The Mochwarts, living in what Schwelb termed "consummate luxury," had not filed federal or state tax returns since 1978 and owed more than $74,000 in back taxes.

That fact, which Mochwart freely admitted, and indeed had brought before the court in order to demonstrate his inability to make high support payments to his wife, so provoked the judge that he rebuked the unhappy couple for "spiritual poverty."

And then, unable to ignore what he termed "the shocking facts of this case," Schwelb took what he said was the "unprecedented" step of inviting tax authorities to intervene in a routine civil proceeding, personally mailing copies of his opinion to the Internal Revenue Service, the U.S. attorney and tax authorities in Maryland and the District.

"The parties," wrote the judge, "have no right to continue to enjoy a luxurious life style when it has not been demonstrated . . . that the taxpayers will be compensated for every penny belonging to them, which Mr. Mochwart has improperly appropriated for his own use and that of his family in order to maintain a largely unearned and ill-deserved affluence."

The judge's fervor, transmitted in an opinion written in July, came as a shock to both parties.

"Since, to my knowledge, inviting the IRS to intervene has never been done before, it would be fair to say everyone was surprised," Mrs. Mochwart's attorney, Peter R. Sherman, said this week.

Not the least of those was Charles E. Mochwart, a 46-year-old insurance broker and founder of his own company, who conceded in court that he had "lived beyond my means" and explained his tax lapses by saying, "I just got behind. It's one of the stupidest things I've ever done."

But Mochwart protested that the judge had painted him all wrong.

"It's a humbling thing for a man to admit he's lived beyond his means," Mochwart said. "I felt like I'd bared my soul up there and deserved fairer treatment than to be depicted as a playboy socialite who'd screwed the community."

Moreover, Mochwart said he showed the judge an agreement he had already worked out with the IRS in June under which he would have his federal tax bill paid off by March 1982.

"That's one of the ironies," Mochwart said. "I showed him documents saying I have dealt with the IRS. I've made every payment I'm supposed to."

Judge Schwelb ordered that $3,200 of Mochwart's $3,700 monthly income be paid for alimony and child support, and also stipulated that the defendant pay a sum owed to the District of Columbia for 1977 personal income tax still outstanding.

"The main thing is for me to get myself out of this damn mess," said Mochwart, whose divorce case also revealed that he and his wife were four payments behind on their mortgage. "I have a really small business and this is the most painful piece of advertising."