Yacht theft is "a helluva lot more common than it was five years ago," and this year's losses may top $60 million, a marine insurance expert testified to a House subcommittee this week.

Robert D. Chapman, of the Insurance Company of North America, said yachts are easy to steal because of the ease with which thieves can erase identifying numbers and because of the lack of coordination among law enforcement agencies.

Frequently, such vessels are used in smuggling drugs to the United States.

These were the problems that the House Coast Guard and Navigation Subcommittee was trying to deal with during a two-day hearing - one day here and another day in New Orleans.

During hours of testimony, subcommittee members heard barrages of complaints about the Coast Guard because of its alleged failure to take action in some of these thefts.

Rep. Mari Biaggi (D.N.Y.), subcommittee chairman, proposed these solutions to the twin problems of hijacking and drug smuggling:

Amending the U.S. Criminal Code to forbid any American to posses an illegal drug beyond what is now the 12 mile limit.

Creating a 50-mile Customs Enforcement Area to let the Coast Guard board all vessels, foreign and domestic, displacing less than 500 gross tons. This tonnage limit would not interfere with 99 per cent of regular legal trade, he said.

Consolidating data among law enfordement agencies.

Settling jurisdictional disputes among these agencies.

Requiring yacht owners to file travel plans when they leave the country and to go through customs when they return.

In testimony here, Rear Adm. Robert W. Durfey, commander of the Seventh Coast Guard District, said the customs requirement already exists.

However, he said, filing travel plans would be impractical because the Coast Guard does not have the personnel to cope with the flood of paperwork that would result from this requirement.

The most notable incident under consideration was the disappearance of the Pirate's Lady, a 75-foot, $1.1 million yacht that vanished after leaving Apalachicola, Fla., Jan. 27. Charles Slater, the New Orleans businessman who owned the Pirate's Lady, did not testify because, he said, "I didn't feel anything I would say in public would be beneficial to the investigation."

Even though federal agencies have stopped their search for his missing yacht, Slater said his search is still going on, although he refused to go into details.

The Pirate's Lady disappeared about three months after the Flying Dutchman, an Alabama owned yacht, vanished after departing from Apalachicola with four persons aboard.

There was almost no testimony about the Flying Dutchman, but Bjorn Johansen, a professional ship finder, told the subcommittee he thinks the Pirate's Lady is "still afloat someplace."

Though he could offer no evidence to support this statement, Johansen said pirates would not destroy such a valuable craft without getting some use out of it. Johansen testified in New Orleans, as did Igantius and Margie Diecidue, parents of David Diecidue, the Pirate's Lady missing deckhand.

Ignatius Diecidue, who suffered a heart attack shortly after the Pirate's Lady vanished, said little as his wife read a statement sharply critical of rescue efforts to find their 20-year-old son, who was aboard the yacht with Tony Latuso, its 47-year-old skipper.

Like Johansen, Mrs. Diecidue said that the Pirate's Lady probably is still afloat. However, she based her belief on the fact tha no debris that might have resulted from the yacht's sinking had been discovered.

"Our hearts are lost in the past," she said as her voice broke frequently, "and we know we cannot go back to effect a rescue.

"We must go forward, as difficult as it is, into the future to seek an answer to this mystery."