WASHINGTON — Conservatives are increasing the pressure on Mitt Romney again.

That Mr. Romney has not yet named his vice-presidential nominee has created an opening for social and economic conservatives to pressure him publicly, and they have taken the opportunity to make an aggressive case for Representative Paul D. Ryan of Wisconsin.

In rallying around Mr. Ryan, a champion of cutting government spending and reining in the costs of programs like Medicare and Medicaid, conservatives are calling for Mr. Romney to select someone who can push their fiscal agenda, but they also are setting the stage for a possible letdown on the right if Mr. Romney chooses someone else in his race against President Obama. A strongly worded Wall Street Journal editorial on Thursday urged Mr. Romney to pick Mr. Ryan, saying he “best exemplifies the nature and stakes of this election.”

The editorial follows a fresh wave of public pressure from other conservative outlets for Mr. Romney to erase doubts about his commitment to conservative causes — an issue that has dogged Mr. Romney since his days campaigning as a liberal Republican for the Senate in Massachusetts.

“The conservative base of the party is so concerned about Obama and his approach to government that they are going to vote for Romney,” said John Brabender, who was Rick Santorum’s chief strategist during his nominating fight with Mr. Romney. “The question is, are they going to make 10 phone calls to their friends and relatives because they care so passionately? That’s going to be somewhat of a challenge.”