TRENTON - A Democratic state lawmaker has introduced a bill that would force Republican Gov.-elect Christopher J. Christie to select a Democrat to replace New Jersey's U.S. senators - both of them Democrats - if either was unable to complete his term.

Assembly Majority Whip John F. McKeon of Essex County said he began to think about procedures to fill a vacant Senate seat after the recent death of Sen. Edward M. Kennedy (D., Mass.).

McKeon's bill, introduced and referred to the State Government Committee yesterday in the final weeks of the legislative session, would require that the governor fill a seat within 30 days after it became vacant and that the appointee come from the same political party as the departed officeholder.

The temporary appointment would continue until the next general election in most cases. If the vacancy occurred within 64 days of the June primary, the appointee would serve until the subsequent November election.

Under current law, the governor can call a special election to fill the vacancy or make a temporary appointment. McKeon said special elections tended to have poor voter turnout and were an unnecessary expense.

"This bill would save taxpayers an estimated $10 million in the cost of an unscheduled statewide election," he said.

"It also would honor the will of the electorate by requiring that the appointee be from the same political party as the U.S. senator elected by voters."

McKeon said his bill would make the process to fill a Senate vacancy similar to processes used to fill vacancies at the local, county and state level.

Maria Comella, spokeswoman for Christie, said the governor-elect had not had a chance to study the bill but would "look closely at any and all legislation that is in the best interests of New Jerseyans."

Gov. Corzine could not be reached for comment yesterday.

McKeon's bill is "clearly a political move to limit the power of Gov.-elect Christie in a potential Senate appointment," according to Joseph Marbach, a political analyst at Seton Hall University.

The change is of particular significance because of the age of U.S. Sen. Frank Lautenberg. New Jersey's senior senator will be 90 when his term ends in 2014.

Most states allow the governor to fill a temporary vacancy without regard to the appointee's political party, Marbach said. He said he thinks such a change would stand up to legal challenges but he is curious how the legislation will be received during the lame-duck session of the Democratic-controlled Legislature.

"It's really the first major test of this notion of bipartisanship that's been talked about," Marbach said. "If it does pass, it's going to mean we won't see much bipartisanship, because it is really an attack on the power of the governor."

The last time a New Jersey governor named someone to fill a vacant U.S. Senate seat was when Corzine appointed U.S. Rep. Robert Menendez to be his own replacement in 2006. Later that year, Menendez, now 55, was elected to a full six-year term.

Lautenberg, 85, was attacked for his age during his most recent campaign, but appears to be active and fit.

"Sen. Lautenberg is focused on continuing his work on behalf of the people of New Jersey in the U.S. Senate regardless of what action, if any, is taken in the state legislature," spokesman Caley Gray said yesterday.

Contact staff writer Adrienne Lu at 609-989-8990 or alu@phillynews.com.

Inquirer staff writer Cynthia Burton contributed to this article.