“By putting the two properties together, we think this can give us the fifth major,” Haggerty said.

That very much remains to be seen. The Davis Cup, which began in 1900, is the premier team tennis competition for men. The Fed Cup, introduced in 1963 and initially known as the Federation Cup, is its counterpart for women. But both have struggled for traction in recent years, with top men’s players frequently skipping and criticizing the Davis Cup.

Haggerty and the I.T.F. board hope to reverse that trend by generating increased buzz and revenue with the new event. The move comes after a board decision earlier this year to address player concerns by reducing Davis Cup singles matches from best-of-five sets to best-of-three sets. But fusing the two events is far from certain to lift the competitions to the degree that Haggerty hopes.

Steve Simon, chief executive of the Women’s Tennis Association, has expressed support for the plan.

“I think it is great, to be honest,” Simon said. “I think the more times our sport is played together, the better we do as a sport. At the highest level, which is at Grand Slam events, the sport is combined, and I think bringing men and women together is what separates us from the other sports. Conceptually, to do that makes a whole lot of sense.”

Martina Navratilova, who won the Fed Cup with her native Czechoslovakia and with the United States after becoming a naturalized American citizen, expressed cautious support.

“Events historically have been better and stronger when it’s both men and women playing together,” she said in a telephone interview. “That’s how the majors started thriving and became much bigger. I’m ambivalent about this because I know women can stand on their own, but it may be for the good of the game. This may be a great idea.”

Haggerty said he had received preliminary support from Chris Kermode, the chief executive of the ATP Tour. But the ATP could soon be in competition with the Davis Cup if it approves a new World Team Cup event that could be started as early as 2019 and would most likely be staged in what is now the off-season.

It is unclear whether the ATP’s proposed new — and potentially lucrative — event would take place every year or every other year. But it could create an awkward situation in which a national team is crowned champion in November at the Davis Cup, and another is crowned champion in December at the ATP event.