Matthew Ryan Williams for The New York Times

After his surprise triple victories in Colorado, Minnesota and Missouri, Rick Santorum has begun soaring among Republican primary voters, erasing Mitt Romney’s lead in the race for the party’s presidential nomination.

A New York Times/CBS News poll released Tuesday morning showed Mr. Santorum surging among Republican primary voters nationwide, lifted by support among conservatives, evangelical Christians and Tea Party supporters.

In the new poll, 30 percent of Republican primary voters say they support Mr. Santorum, compared with 27 percent for Mr. Romney. While Mr. Santorum’s lead is essentially a tie with Mr. Romney because it is within the margin of sampling error, it reflects a significant jump for him from earlier polls.

The two other major candidates are further behind, at 12 percent for Ron Paul and 10 percent for Newt Gingrich. Mr. Gingrich’s numbers have fallen sharply since his win in South Carolina on Jan. 21.

In the last poll by The Times and CBS News about a month ago, when voters were asked a slightly different question, just 16 percent said they preferred Mr. Santorum while 21 percent backed Mr. Gingrich. Leading the field back then was Mr. Romney, with the support of 28 percent of Republican primary voters.

The poll is the latest example of the tremendous instability that has marked the Republican nominating contest, in which candidates have repeatedly shot up in popularity and then plummeted.

Mr. Santorum’s bump is largely fueled by increased support from self-described conservatives, evangelical Christians and Tea Party supporters. The poll shows Mr. Santorum, a former Pennsylvania senator, backed by nearly four in 10 voters from each of these groups; last month, no candidate was the clear favorite among these voters.

At the same time, another result in the poll underscores the race’s continuing fluidity. A majority of voters (six in 10) who expressed a candidate preference said they could still change their mind – down from 74 percent who said so a month ago, but enough to potentially mix things up again.

Two polls released on Monday, by the Pew Research Center and Gallup, also showed Mr. Santorum’s sharp advance in the field.

The nationwide poll is based on telephone interviews conducted Feb. 8-13 on landlines and cellphones with 331 Republican primary or caucus voters, and has a margin of sampling error of plus or minus five percentage points. Additional results from this poll will be available after 6:30 p.m. Tuesday at NYTimes.com.