TAMPA, Fla. — Even as Mitt Romney and Representative Paul D. Ryan exhort Republicans to embrace their proposed Medicare changes and spending cuts, the party’s rank and file is growing less enthusiastic about the fight than the top of the ticket.

Republican lawmakers and candidates are distancing themselves from the Ryan budget plan, which helped make the proposed changes a national issue. Republicans say the party now belongs to the more senior — and historically more malleable — member of the ticket, Mr. Romney, and not Mr. Ryan, the younger conservative firebrand who has become the subject of repeated Democratic criticism.

“The plan is the Romney plan,” said Senator John Hoeven, Republican of North Dakota. “He’s the one that’s going to drive the agenda.”

The distancing ranges from subtle to stark. Some first-time House candidates, unencumbered by a vote on the Ryan plan, have told local news media outlets that they have not and will not endorse the proposals found in the vice-presidential nominee’s budget. Some veteran lawmakers who voted for the plan are demurring on whether it will be the party’s policy blueprint, while the few in tough races who voted against it have made their opposition a calling card.