While the Senate this week will be dominated by talk of last week’s terrorist bombings in London and the United States’ own homeland security spending priorities, battles over the Supreme Court, stem-cell research and gun manufacturers’ liability will be bubbling under the surface during the three weeks leading up to the long-awaited August recess.

Though speculation on Supreme Court retirements and possible nominees has become the hottest parlor

game in town, Senate Majority Leader Bill Frist (R-Tenn.) and Senate Minority Leader Harry Reid (D-Nev.) each continue to keep one eye on other legislative issues, including the issue of how to bring up one or more controversial stem-cell research bills.

So far, however, centrist Senate Republicans and Democrats sponsoring a broad stem-cell research bill are resisting Frist’s attempts to give conservative and center-right Senators political cover on any stem-cell vote by loading up the Senate calendar with various alternatives dealing with issues ranging from bone marrow extractions to chimeras.

Instead, Democrats and moderate Republicans are pushing for unfettered Senate passage of a House-passed bill that would allow federal funding for stem-cell research on donated embryos already slated for destruction. An executive order penned by President Bush prohibits federal funding of research on any stem-cell lines derived after Aug. 9, 2001 — a policy social conservatives have lauded as protecting the lives of the unborn, but one which many scientists have complained is too restrictive to produce the life-saving therapies they believe could develop from stem-cell experimentation.

While Reid and the bill’s Senate GOP sponsors, Sens. Arlen Specter (Pa.) and Orrin Hatch (Utah), continue negotiations with Republican leaders, they have so far refused to accept a proposal for a unanimous consent request Frist floated last week, according to sources. The UC would allow votes on six separate bills — each requiring 60 votes for passage — including the House-passed stem-cell research measure and two bills pushed by right-to-life activists which would ban all forms of human cloning and the creation of genetic animal-human hybrids, or chimeras.

The UC also would allow votes on a measure to encourage stem-cell recovery from bone marrow and umbilical cord blood; a Frist bill to promote research into stem-cell extraction that would not harm embryos; and a Sen. Kay Bailey Hutchison (R-Texas) modification of the House bill. (Hutchison’s office did not return calls as of press time Monday.)

Though a bone marrow and cord blood bill has already passed the House, all three of those bills have caused the most concern among Democrats and centrist Republicans who fear they will siphon off potential swing votes and doom the House bill. That is, before Bush can veto it, as he has threatened to do.

“These other bills are being thrown out there … to peel away votes and to confuse,” said one Republican operative who backs the House-passed legislation.

Alison Dobson, spokeswoman for stem-cell research supporter Sen. Tom Harkin (D-Iowa), agreed.

“This shouldn’t be about political cover,” she said, arguing that the alternatives being pushed by Frist and other conservatives are “speculative” and a failure to enact the House bill could “put lifesaving research on hold for 10 years.”

To underline that point, stem-cell research backers plan to hold a press conference Wednesday with actor Michael J. Fox, who suffers from Parkinson’s disease, and Dana Reeve, whose husband, actor Christopher Reeve, died years after suffering a debilitating spinal cord injury. Fox and Reeve are expected to urge wavering Senators to support passage of the House bill over other alternatives, because they believe current stem-cell research methods that require the destruction of embryos could help scientists find cures to myriad diseases.

Meanwhile, the Republican Main Street Partnership is considering running ads in as many as six states, including Mississippi and Virginia, to pressure fence-sitting Senators to vote for the House bill, said a spokesman. The ads do not mention specific Members by name and instead urge viewers to “call Congress and tell them you support embryonic stem-cell research.” RMSP ran the same ad in advance of the House vote in May.

If a vote is held on only the House bill, Senate Democratic leaders insist that by the time of a vote all 44 Democrats and Vermont Independent Jim Jeffords will support it, said the Republican operative. However, only 33 Democrats, eight Republicans and Jeffords are firmly in favor of the measure. Eleven Senators — six Republicans and five Democrats — are “leaning yes,” while seven Republicans and one Democrat appear undecided, the operative said.

Though Frist had tentatively scheduled stem-cell votes for this week, those will likely be pushed back to next week because the debate on the Homeland Security spending bill is expected to last much longer than originally planned, given renewed fears in the United States about terrorist attacks.

Indeed, it’s no secret that Democrats plan to use this week’s debate to bring up old grievances with the Bush administration’s homeland security spending priorities.

Chiefly, Sen. Charles Schumer (D-N.Y.) will be raising the specter of London as he presses for more funds to beef up security for mass transit and railroads. But both Democrats and Republicans are expected to offer amendments to better protect potential terrorist targets in their states.

Meanwhile, Senate Republicans are also gearing up for a mid-month battle over a bill to absolve gun manufacturers from liability in firearm-related deaths or injuries.

Before the July Fourth recess, Frist said he expected consideration of the measure to go much more smoothly than it did last year.

“We’re going to pass it, and we’ll pass it in a very reasonable period of time, and it’ll have broad bipartisan support,” he said.

Frist has good reason for such optimism. The measure has 56 co-sponsors, including seven Democrats, and shifts in the Senate’s makeup may make it easier for Frist to beat back gun control amendments that scuttled the measure last year.

While Sen. Dianne Feinstein (D-Calif.) is likely to offer her amendment to extend the ban on assault weapons for 10 years, she may not be able to break the 50-vote mark this time around. Though she prevailed last year on a 52-47 vote, six of her supporters have since left the Senate, and pro-gun rights Republicans replaced five of them.

Sen. John McCain (R-Ariz.) may be missing a similar number of votes from the tally last year on his amendment to require FBI background checks for buyers at gun shows.