President Obama will sign a presidential memorandum on Wednesday to extend benefits to same-sex partners of federal employees, administration officials said Tuesday evening, but he will stop short of pledging full health insurance coverage.

Mr. Obama, in an Oval Office announcement, is expected to offer details about which benefits will be provided. It is the most significant statement he has made on gay issues, and it comes as he faces intense criticism from several gay rights leaders over what they suggest has been a failure to live up to campaign promises in the first months of his presidency.

Mr. Obama will be weighing in for the first time on one of the most delicate social and political issues of the day: whether the government must provide benefits to same-sex partners of federal employees. While he will announce a list of benefits, officials said, they are not expected to include broad health insurance coverage, which could require legislation to achieve.

The initial reaction from some gay rights advocates was mixed.

“Extending benefits to partners of gay federal employees is terrific, but at this point he is under enormous pressure from the gay civil rights community for having promised the moon and done nothing so far,” Richard Socarides, an adviser to the Clinton administration on gay issues, said Tuesday evening. “So more important now is what he says tomorrow about the future for gay people during his presidency.”