(Adds details on second case)
By Andrew Chung and Lawrence Hurley
WASHINGTON, Oct 1 (Reuters) - The short-handed U.S. Supreme Court launched its new term on Monday, with the legal arguments in its stately courtroom overshadowed by the harsh fight over President Donald Trump's nomination of Brett Kavanaugh for a lifetime job as a justice.
On the surface, it looked like business as usual for the high court, except that there were eight justices on the bench, not the usual nine, following the retirement of long-serving conservative Justice Anthony Kennedy, effective in July. Trump selected Kavanaugh to replace Kennedy, but the Senate confirmation process has been detoured as the FBI investigates sexual misconduct allegations against the nominee.
There was no mention of the ferocious confirmation battle as the justices heard arguments in two cases, kicking off a term running through June.
The difficulties facing the court now that it is - at least temporarily - evenly divided ideologically with four liberals and four conservatives were on full display in the first of the two cases. Kavanaugh's confirmation would restore and deepen conservative control of the court.
A 4-4 split is possible in the case, a property rights dispute brought by timber company Weyerhaeuser Co seeking to limit the U.S. government's power to designate private land as protected habitat for endangered species. The dispute focused on the dusky gopher frog, an amphibian protected under the federal Endangered Species Act.
Weyerhaeuser harvests timber on the Louisiana land in question and is backed in the case by business groups including the U.S. Chamber of Commerce. Weyerhaeuser challenged a lower court ruling upholding a 2012 U.S. Fish and Wildlife Service decision to include private land where the frog does not currently live as critical habitat, potentially putting restrictions on future development opportunities.
The case pitted property rights against federal conservation measures. The frog, found only in four locations in southern Mississippi, also previously inhabited Louisiana and Alabama.
While the liberal justices appeared sympathetic to the government's defense of the critical habitat designation, the conservatives seemed to lean toward the property owners.
"We know that habitat isn't just where a species lives. ... It's also where a species could live," liberal Justice Elena Kagan said.
Conservative Justice Samuel Alito said that although some people may not "shed tears for a big corporation" like Weyerhaeuser being forced to spend money to benefit frogs, the law would apply equally to a family farm.
A 4-4 ruling, as is possible in this case, leaves lower court decisions in place and sets no nationwide legal precedent. If Kavanaugh is confirmed, the court could decide to rehear the case with a full complement of justices.
The second case involved the scope of a federal law that outlaws discrimination on the basis of age.
Firefighters John Guido and Dennis Rankin, who were 46 and 54 years old respectively at the time, were fired in 2009 from their jobs at the Mount Lemmon Fire District, near Tucson, Arizona. They were the district's oldest full-time employees.
Guido and Rankin sued, saying the fire district had violated the Age Discrimination in Employment Act. The dispute centers on whether that law applies to state and local government entities regardless of size, or whether those with fewer than 20 employers like this one are exempt, as private employers are.
Most of the justices on Monday seemed inclined to uphold a lower court ruling in favor of the firefighters.
Chief Justice John Roberts began the day's proceedings by congratulating Justice Ruth Bader Ginsburg, at age 85 the oldest of the justices, for her "distinguished service" during a quarter century on the court.
Before hearing their first arguments, the justices issued a list of cases they were accepting and rejecting. Among them, they rejected Bill Cosby's bid to avoid a defamation lawsuit brought by a well-known former model, Janice Dickinson, who said the comedian sought to destroy her reputation after she publicly accused him of rape.
Trump nominated conservative federal appeals court judge Kavanaugh in July. The FBI investigation, ordered by Trump on Friday under pressure from moderates in his own party, is due to last no more than a week.
Trump on Monday said he wanted the FBI investigation to be comprehensive, but quick, and not a "witch hunt."
Reporting by Andrew Chung; Additional reporting by Lawrence Hurley; Editing by Will Dunham