Mr. Dietl secured the endorsement on Monday of a city councilman, Eric A. Ulrich, who had considered a mayoral run himself and is one of only three Republicans in the 51-member body — a modest help to Mr. Dietl’s efforts to win party backing. “I’ve been a lifelong Republican my whole life,” Mr. Dietl said at a news conference with Mr. Ulrich.

The jockeying for position at the front of a growing pack will be on full display on Wednesday night as the candidates present their cases during a screening of candidates on the Upper East Side by the Manhattan Republican Party and the party’s leaders from other boroughs.

The lineup will also include Mr. Massey, a former real estate sales executive who has demonstrated an ability to raise — and spend — significant money, and the Rev. Michel J. Faulkner, a Harlem pastor and a former New York Jets player. Ms. Malliotakis is expected to be part of the event as well.

“Someone up there is going to be our nominee,” Ms. Malpass said. “I am truly undecided. I am waiting to see them present their vision of the city Wednesday and how they plan to make Bill de Blasio a one-term mayor.”

Mr. Catsimatidis is unlikely to be at the screening; he continued to hold back from declaring a run and in recent days has appeared unlikely to jump into the race. (Ms. Malpass said if he did declare before Wednesday evening, he could still take part.)

The addition of Ms. Malliotakis adds a new dynamic to a race already complicated by the candidacy of Mr. Dietl, who had been seen as a wild-card alternative to Mr. de Blasio despite his florid and occasionally profane language and the wide target presented by his past tax issues and work for Fox News.