Many of the well-heeled who snapped up thousands of new condominiums in Washington in the last three years are now claiming that they have been victims of expensive but shoddy workmanship: roofs that leak, ceilings that sag, heating systems that go dead in deep winter and airconditioners that break down in steamy July.

Former Sen. George McGovern, Amtrak president Alan Boyd, former presidential adviser virginia Knauer and other owners at 2029 Connecticut Ave. NW, have filed a $3 million lawsuit charging that their developer, Conrad Cafritz, left them with sagging and cracking ceilings.

Up the street at Cathedral Park, 3100 Connecticut, where one-bedroom condominums now sell for more than $100,000, the owners are replacing most of the ceilings in the apartments on the top floor because green wood used in the attic during the building's renovation has warped.

Farther up the street, the diplomats, lawyers and others who live at 3701 Connecticut have filed a $2.5 million lawsuit against their developer, alleging that the roof leaks, the heating system doesn't always work and that the central air-conditioning system must be scrapped and replaced.

Twenty-five percent of the 14,851 converted and new properties have or will experience warranty problems with the roof, heating or airconitioning systems, or plumbing or wiring systems, said Robert L. Beall, a vice president at Legum and Norman, one of the city's largest condominium management firms.

Art Hiban of Shannon and Luchs, agreed with Beall's 25 percent estimate.

Although the city's condominium law, one of the toughest in the nation, requires developers to give prospective buyers engineering reports on the condition and life expectancy of the vital systems in the buildings, these reports "are usually shallow and don't tell you much," Hiban said.

James Stanford vividly recalls that two months after he moved to his $62,000 South Brook Court condominium on 16th Street, "one wonderful Saturday morning I woke up to the dripping of water and went to my kitchen to find a big flap of plaster hanging from the ceiling and water coming in quite fast."

The building's roof leaked, he said. Then there was the brownish colored rash on his living-room wall that came from moisture seeping in around an improperly caulked vent. The developer made the repairs, he said.

"You feel like you've been had," said Jack Murphy, administrative assistant to Sen. Barry Goldwater (R-Ariz.) and president of cathedral Park where ceilings in 40 apartments on the top floor are bing braced or replaced.

With city condominium prices sometimes in six figures, the purchasers, who included senators, congressmen, judges and top White House and Capitol Hill staffers, expected the units "to be perfect in all substantial respects," said Devin J. Doolan, an attorney who now represents some of the buyers.

Many of the buildings that people bought into two and three years ago in the midst of condomania were old and suffering from neglect because of high operating costs and rent control, said several real estate sources.

While some developers did extensive and quality renovations, Beall said, others simply cashed in on the boom with primarily cosmetic revovations. Then "zealus sales agents" painted a life of almost trouble-free living that was reinforced by the high prices, said Beall.

Some in the real estate industry said the problem will probably grow because of the large number of buildings converted to condominiums in the last two years.

Although only 395 apartment units were converted in 1977, the number jumped to 1,918 in 1978 and tripled to 4,287 in 1979, city records show. Figures for 1980 were unavailable.

Hiban said that Shannon and Luchs recommends to its condominium clients that they hire their own engineers to evaluate the condition of the "big ticket items," such as the roof, the pluming and heating systems and the wiring.

Many of the disgruntled occupants contend that the faulty workmanship should be covered in the two-year warranties mandated by city law, but developers often disagree.

Mike Brenneman, a leader in condominium sales and conversions (he sold the units at 2026 Connecticut), angrily defended the developers work.

"I question some of the things that I'm hearing that developers' have done badly or did not do at all," he said. "The perception of the problem is nothing more than that. . . . It is my opinion that most of the conversions have been done credibly," although there might be "imperfections here and there."

Although some of the fault apparently lies with the developers, Doolan, Hiban and others also believe some buyers have unreasonable expectations of condominium life. "People must realize when they are buying used housing there will be problems," said Doolan. "Since it is not new, your expectations have to be somewhat different."

At 2029 Connecticut, where the 26 owners make up a virtual Washington's who's who -- Amtrak president Boyd, McGovern, Rep. Lindy Boggs, (D-La.) and Knauer -- residents have alleged that developer Conrad Cafritz left them with "plaster ceilings in some or all of the condominium units requiring repair, renovation, restoration or replacement."

Cafritz contends that he sold the 26 units in the 1917 building in an "as is" condition in 1977 after making some repairs and now he is being asked to guarantee "against any and all unexpected problems resulting from the age of individual building components."

The owners of the 206 units at 3701 Connecticut Ave. alleged in their suit, filed last April, that the developers, Marcel, Stephen and Robert Weiss, all of New York, reported a useful life remaining for the building's major components that was "inflated, excessive, inaccrate and misleading."

The Weiss brothers denied the allegations and said that any losses or damages were the result of "negligence, improper or inadequate maintenance, alteration or normal wear and tear or accident" caused by the new owners.

Fred Fitzgerald, a lawyer for the Federal Communications Commission and president of the condominium owners association, said the new owners have paid out almost $80,000 to patch the air conditioning system, buy new boiler parts and make other repairs.

And beginning last month, each owner started paying an additional $104 a month on top of the average $200 condominium fee to finance the replacement of the central airconditioning system.

Mark Sager, who lives on the top floor, recalled that last summer, "it was so unbearable one night I sat in the bathtub and I thought of going to a hotel." The air-conditioning system breaks down often, said Sager, an insurance agent, who paid $75,000 for his two-bedroom unit.

At Cathedral Park, however, the owners can no longer sue their developer under a settlement they made with the company two years ago in which it agreed to make other repairs in the building including replacing the boiler.

With the growing dissension about warranty problems, the Community Association Institute, a private organization of homeowners, condominium developers and managers, lawyers and public officials will hold a forum Feb. 24 at the Tysons Westpark Hotel on Rte. 7 in Tysons Corner to discuss the ways that condominium owners and developers can resolve their disputes short of costly court battles.