TAMPA, Fla. — The rising presidential candidacy of Gov. Rick Perry of Texas is stirring excitement for many Republican voters but is creating unease in some quarters of the party’s establishment, particularly over his views of Social Security, which are at the root of an intensifying competition with Mitt Romney.

The decision on Monday by Tim Pawlenty, a former Republican presidential rival, to support Mr. Romney’s campaign signals the beginning of an effort by some party leaders to try to slow the ascent of Mr. Perry — or to push him to explain positions that are considered provocative.

In announcing his endorsement on Monday, Mr. Pawlenty said he believed Mr. Romney was the only candidate with the “unique qualifications to confront and master our severe economic predicament.” The judgment of Mr. Pawlenty, who dropped out of the presidential race last month, was carefully watched by some Republicans because he knows both men well.

The endorsement was a visible marker in a quietly continuing battle for the soul and direction of the Republican Party between traditional party leaders and grass-roots conservatives. To some degree it is a clash of styles and of principle versus pragmatism, but it also encompasses foreign and domestic policy differences, some of which have surfaced as the presidential campaign has intensified.