WASHINGTON — Senator Clinton will concede tonight that Senator Obama has the delegates to secure the Democratic nomination, campaign officials said, effectively ending her bid to be the nation’s first female president.

Mr. Obama is 40 delegates shy of clinching the nomination, but he is widely expected to make up the difference today with superdelegate support and votes in South Dakota and Montana. Once he reaches the magic number of 2,118, Mrs. Clinton will acknowledge that he has secured the necessary delegates to be the nominee.

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The former first lady will stop short of formally suspending or ending her race in her speech at New York City.

She will pledge to continue to speak out on issues like health care. But for all intents and purposes, the two senior officials said, the campaign is over.

Most campaign staff will be let go and will be paid through June 15, said the officials who spoke on condition of anonymity because they were not authorized to divulge her plans.

The advisers said Mrs. Clinton has made a strategic decision to not formally end her campaign, giving her leverage to negotiate with Mr. Obama on various matters including a possible vice presidential nomination for her. She also wants to press him on issues he should focus on in the fall, such as health care.

Universal health care, Mrs. Clinton’s signature issue as first lady in the 1990s, was a point of dispute between Mr. Obama and the New York senator during their epic nomination fight.

Mrs. Clinton was at home in Chappaqua, N.Y., with her husband, President Clinton, and was placing calls to friends and supporters.

On NBC’s “Today Show,” the Clinton campaign chairman, Terry McAuliffe, said that once Mr. Obama gets the majority of convention delegates, “I think Hillary Clinton will congratulate him and call him the nominee.”

In a formal statement, the campaign made clear the limits of how far she would go in tonight’s speech. “Senator Clinton will not concede the nomination,” the statement said.

Mrs. Clinton field hands who worked in key battlegrounds said they were told to stand down, without pay, and await instructions. Speaking not for attribution because they didn’t want to jeopardize their jobs searches, many said they were peddling resumes, returning to their hometowns, or seeking out former employers.

Clinton officials have said they would not contest the seating of Michigan delegates at the convention in Denver this August. The campaign was angry this past weekend when a Democratic National Committee panel awarded Mr. Obama delegates it thought Mrs. Clinton deserved.