WASHINGTON (AP) — With time and tempers short, everyone’s playing hardball in the drive to pass — or stop — President Barack Obama’s massive health care legislation by the weekend.

Business groups are spending $1 million a day to depict the bill as a job killer in television ads in the home districts of 26 wavering House Democrats. A new ad barrage from supporters of the legislation went up Tuesday in 11 districts, some overlapping. And unions are threatening some of those lawmakers to come through for Obama — or pay the price in the fall elections.

Obama has summoned members to the White House one by one for private, face-to-face persuasion, and also met larger groups. White House aides said he plans at least one more public health care event this week, including remarks in Fairfax, Va., on Friday. Diverse administration resources are being employed: Even the Navy secretary is in the game.

“We here in Congress are giving a new meaning to March madness,” Sen. Lisa Murkowski, R-Alaska, an opponent of the legislation, said Tuesday.

At stake is a bill that would cover some 30 million uninsured people, end insurance practices such as denying coverage to those with a pre-existing conditions, require almost all Americans to get coverage by law and try to slow the cost of medical care nationwide.

The comprehensive legislation could affect nearly every American, from those undergoing annual checkups to people facing major surgery.

Activists on both ends of the political spectrum are energized. Tea party volunteers, who rallied Tuesday in Washington, are planning to flood congressional offices with e-mails opposing the legislation as a step toward socialism. And some on the political left have joined in calling for the bill’s defeat because it leaves out a federal insurance option.

The sought-after Democrats — mainly moderates, but also a few liberals — are mostly trying to stay out of sight. They include 37 who voted against the bill last year and a smaller number who are having second thoughts after supporting it the first time. Walking briskly, lawmakers duck in and out of the House chamber during votes, avoiding eye contact with reporters.

Moderate Rep. Mike McMahon, D-N.Y., is feeling the push and pull. Elected with strong labor support two years ago, he voted against the bill in November, pleasing constituents in his Republican-leaning district on Staten Island who saw it as a government power grab.

Last week, McMahon received a visit from Mike Fishman, president of the ServiceEmployees International Union’s local 32BJ. The blunt message: If you can’t support health care reform, we can’t support you.

The union is threatening to switch its allegiance if he votes against the bill. “Everyone will be looking very, very closely at this vote,” Fishman’s spokesman, Matthew Nerzig, said with understatement.

At the White House on Tuesday, Obama met with health care executives, including Sister Carol Keehan, head of the Catholic Health Association. In a break with other abortion opponents, the Catholic hospitals are advocating for the bill.

“We think the bill as written now meets the test of no federal funding for abortion,” Keehan said in an interview. She’s letting anti-abortion Democrats know her position announced over the weekend.

An estimated $200 million has been spent for political advertising on health care since the beginning of last year, with groups favoring Obama’s overhaul holding a slight edge. In the final stretch, however, opponents have gotten the upper hand and supporters are rushing to catch up.

A coalition of business groups led by the U.S. Chamber of Commerce went up with ads last week. The group is now spending an estimated $1 million a day, enough for 25 to 40 television ads, said Evan Tracey, president of Kantar Media-CMAG, which tracks political advertising. The ads frame the health care bill as a drag on the economy, raising taxes and saddling companies with expensive new mandates.

Liberal groups are hoping they won’t be too late. Health Care for America Now and several labor unions have announced a $1.7 million ad buy focusing on the districts of 17 undecided Democrats. Their ads portray the health insurance industry as a profit-hungry predator.

“The ads are designed to get people fired up, so that members feel it coming back from their districts,” said Tracey. “Members are on notice that they may be voting on this now, but their constituents will be voting on it in November.”

House Democratic leaders are still short of the 216 votes they need. While broad outlines of the $1 trillion, 10-year measure are well known, critical final details are still being ironed out. Lawmakers are awaiting a cost report from the Congressional Budget Office on compromises worked out with Obama to reconcile versions passed earlier by the House and Senate.

Democratic leaders are considering using a legislative procedure that would allow them to pass fixes to the Senate bill without taking a direct vote on the underlying legislation. The maneuver is a kind of legislative fig leaf to spare House Democrats from directly voting to approve a Senate bill many of them had bitterly criticized. While Republicans also used the tactic when they controlled the House, they are indignant that Democrats would employ it on legislation of such significance.

The crucial group of some three-dozen House Democrats is split roughly into two camps: those who possibly could switch their earlier “yes” votes to “no,” sinking the legislation, and those who might switch from “no” to “yes,” salvaging it.

Then there’s Rep. Bart Stupak of Michigan, who says he has a dozen lawmakers ready to vote against the bill unless it incorporates a tougher firewall against taxpayer-subsidized abortion coverage, although his numbers seem to be dwindling. Stupak said Tuesday he has received only gentle overtures from the White House so far.

Democratic leaders have assigned House Energy and Commerce Committee Chairman Henry Waxman, a California liberal, to negotiate with Stupak, and the two men talk daily.

Stupak said a few of his anti-abortion colleagues have been called by high-ranking administration officials. Ohio Rep. Marcy Kaptur, who backed the bill in November but is undecided now, said she has heard from several Cabinet secretaries.

Another one, a member of the House Armed Services Committee, was surprised to hear from Navy Secretary Ray Mabus, said Stupak, who declined to identify the lawmaker.

• Ricardo Alonso-Zaldivar