On St. Patrick’s Day, Senator Clinton is scheduled to appear in Houston with an African-American congresswoman, Sheila Jackson Lee, and to attend a conference of black churches in that city.

Earlier this week, she put forward a bill to establish a museum on an African burial ground in Lower Manhattan. That follows a Congressional resolution she sponsored in February commemorating the 98th anniversary of the NAACP. In the past two months, she has also celebrated the enactment of a law creating a statue in the Capitol to honor the slave-turned-abolitionist Sojourner Truth, held a celebration to honor African-American leaders in New York, paid tribute to the civil rights movement at a church in Selma, Ala., and spoke to largely black audiences at three campaign stops in South Carolina.

The flurry of recent appeals, appearances, and announcements is being interpreted by some analysts as a sign that Mrs. Clinton has been working to burnish her standing with African Americans and to ward off the threat Senator Obama of Illinois poses to her bid for the Democratic presidential nomination.

A scholar at a think tank that studies African-American issues, David Bositis of the Joint Center for Economic and Political Studies, said signs of inroads by Mr. Obama have prompted Mrs. Clinton and others to press hard for the black vote.

“At the beginning, the Obama boomlet was mostly about whites, but he clearly has caught on among a lot of African Americans. That’s scary for his opponents,” Mr. Bositis said. “The fact is the black vote is real, real important in the Democratic primaries and you can’t underestimate the significance of the black vote.”

“Senator Clinton is following the advice many of us have always given,” an African-American political operative who ran Vice President Gore’s presidential campaign in 2000, Donna Brazile, said. “Campaign early for support, go to the community often and make a case for their support, and turn them out.”

Mr. Obama’s candidacy is a particular danger to Mrs. Clinton because her campaign had hoped to use a flurry of early primaries in large states to cement her front-runner status, even if she stumbled in Iowa and New Hampshire. Now, a series of states with large African-American populations, including New York, New Jersey, Georgia and Illinois, are considering holding primaries on February 5.

South Carolina, which will vote three days before that, could be a barometer. About 50% of primary voters there are expected to be black. “I expect Obama will do better than Hillary,” Mr. Bositis said.

Some of Mrs. Clinton’s intense advocacy in recent days may have been aimed more at civil rights leaders than the general public. Mr. Obama lacks strong ties in the national civil rights community and the former first lady’s actions could dissuade any in that group who may be flirting with the idea of endorsing the Illinois senator.

A spokesman for Mrs. Clinton, Howard Wolfson, said the frequency of recent events with African-American themes was not unusual, especially with the month of February involved. “It’s black history month,” he observed.

Mr. Wolfson noted that, with the exception of the resolution saluting the NAACP, all of the other announcements involved legislation Mrs. Clinton has a history of supporting. “These are things she has done before,” he said.

Recent polls have shown Mrs. Clinton and Mr. Obama in close contention for the black vote. In an ABC/Washington Post poll taken soon after his formal announcement in February, Mr. Obama led Mrs. Clinton, 44% to 33%, among African-Americans expected to vote in the Democratic contest. In a Time magazine survey out this week, the two candidates each had 40% support among blacks.

Another point of concern for Mrs. Clinton was the apparent tightening of the race in the South, where the Time poll showed the Illinois senator lagging his New York colleague by just 5%.

Mrs. Clinton’s pollster, Mark Penn, told The New York Sun yesterday that the Time survey is out of line with three other national polls taken recently, all of which show the former first lady doing substantially better across the board. He also said the proportion of independent voters in the Time poll, 25%, was too high and skewed the results against Mrs. Clinton, who does best with registered Democrats.

Mr. Penn said state-by-state surveys suggest Mrs. Clinton’s recent outreach to African-Americans is paying off. “In the polls I’ve seen in Alabama and South Carolina, she’s gone up after Selma. That is an important indicator of a trend,” he said.

The polls also show some dangers for Mr. Obama, whose campaign declined to comment for this article. A CNN survey out this week showed Mrs. Clinton’s support firm and his support soft.

While 32% of Mr. Obama’s backers said they would “definitely” vote for him, 67% of said it was possible they would change their minds. Mrs. Clinton’s numbers were a virtual mirror image, with 60% pledging definite support and just 39% open to other candidates.

Mr. Bositis said Mr. Obama’s appeal to black voters could erode rapidly if they become convinced he can’t win. “No group is less interested in symbolism than African Americans,” he said, noting that blacks tend to be poorer and therefore more directly affected by social ills and cuts in government programs. “More than anything else, what African Americans want is a winner. The other stuff is like eye candy.”