Sen. Hillary Rodham Clinton (D-N.Y.) is returning to the Senate Tuesday for the first time since suspending her presidential campaign, cutting short her initial plans for a monthlong absence to help her party with critical votes.

Her first appearance after the 18-month-long campaign comes as the Senate has a number of crucial votes expected in the final days before lawmakers depart for the Independence Day recess. Final action is expected this week on the emergency war-spending bill, an overhaul of the Foreign Intelligence Surveillance Act (FISA) and housing legislation — with an outside chance on a Medicare package, too.

Clinton had originally planned to be gone for a month after ending her campaign, according to senior Democratic aides. The New York senator phoned Senate Majority Leader Harry Reid (D-Nev.) after her June 7 concession speech and told him she would be out of the chamber until senators reconvene from the Independence Day break, on July 7 or 8, according to the aides.

Philippe Reines, a spokesman for Clinton, suggested that telephone conversation did not take place in an e-mail to The Hill and refused to confirm her schedule for the week.

However, her staff has said she would return for a couple days before leaving again to campaign Friday with Sen. Barack Obama (D-Ill.) in Unity, N.H — their first joint appearance since Obama became the presumptive nominee.

The two had been engaged in a long and fierce primary battle, which did not end until Clinton bowed out at the beginning of the month. Many Democrats have been concerned about bringing the party together after the prolonged fight that appeared to have pitted core constituencies against each other.

The campaigns chose the venue for their “Unite for Change” event to show that they are in the general-election battle together. Clinton had vowed to do whatever she could to help Obama take the White House in November.

To add to the symbolism, the Obama campaign noted that both candidates had received an equal amount of votes in the town when New Hampshire held its primary in January. Clinton won the state after many polls and pundits predicted an Obama victory.

The joint appearance will likely also renew speculation regarding a “unity” ticket. Many of Clinton’s supporters would like to see the former first lady as Obama’s running mate.

Her attendance in the Senate could prove critical with the FISA and Medicare votes. Democrats hold only a 51-49 majority in the chamber and are already being forced to do without Sens. Edward Kennedy (D-Mass.) and Obama.

Obama has notified Reid that he is available for a small window of time on Thursday afternoon, according to multiple Democratic sources, but leaders may need him earlier depending on the flow of legislation.

The chamber’s Medicare package may be the week’s closest call. The bill is intended to prevent a 10.6 percent payment cut for doctors that is planned to take effect in July, and replace it instead with a small payment hike. A Senate bill in the works would also include a $4 billion boost in improvements for Medicare patients.

Finance panel Chairman Max Baucus (D-Mont.) is negotiating with the committee’s ranking Republican, Chuck Grassley of Iowa, on the Senate bill, but leaders are also watching the Medicare bill being debated in the House.

Aides say if the House’s Medicare bill passes by a wide, bipartisan margin, Baucus and Grassley may be pressured into adopting it instead of introducing their own version.

“It really depends on how strong the support ends up being,” one Democratic source said. “It would be hard for Baucus and Grassley to push forward their own version if the House overwhelmingly supports [its] version.”

Jeffrey Young contributed to this article.