A working group of senators from both parties is nearing agreement on broad principles for overhauling the nation’s immigration laws, representing the most substantive bipartisan effort toward major legislation in years.

The three Democrats and three Republicans, who have been meeting quietly in recent months, plan to announce a final agreement as early as next Friday.

The move would amount to the first tentative step toward comprehensive immigration reform after long-standing gridlock on the issue. The new effort was spurred in large part by the growing influence of Latino voters who strongly backed President Obama and other Democrats in November.

Obama has also called immigration reform one of his top legislative priorities and is launching his own public campaign on the issue next week in Nevada. But a significant number of Americans, particularly within the Republican Party, remain opposed to laws that would make it easier for illegal immigrants to stay in the country or obtain legal status.

The senators are expected to call for normalizing the status of the nation’s 11 million undocumented immigrants, including allowing those with otherwise clean criminal records to obtain legal work permits, officials said. The group is also likely to endorse stricter border controls and a better system for employers to verify the immigration status of workers.

Sen. Charles E. Schumer (D-NY) speaks at President Obama’s inauguration on Monday. Schumer is one of a bipartisan group of senators developing broad principles for overhauling the nation’s immigration laws. (Justin Sullivan/GETTY IMAGES)

It was not clear, however, whether the final agreement will offer guidance on perhaps the thorniest issue in the immigration debate: what mechanism illegal immigrants could use to pursue full citizenship.

“We have basic agreement on many of the core principles,” Senate Majority Whip Richard J. Durbin (D-Ill.), a member of the group, said this week. “Now we have to draft it. It takes time.”

Other senators involved in the talks are Democrats Charles E. Schumer (N.Y.) and Robert Menendez (D-N.J.) and Republicans Lindsey O. Graham (S.C.), John McCain (Ariz.) and Marco Rubio (Fla.).

Two others, Sens. Jeff Flake (R-Ariz.) and Michael F. Bennet (D-Colo.), have also been involved in some of the discussions.

Congressional aides stress that a final agreement has not yet been reached. But the negotiations mark the most in-depth immigration talks involving members of both parties since a similar attempt broke down in 2010 without producing a bill.

McCain, who spearheaded an earlier failed effort in 2007, said Republican attitudes have dramatically shifted since the party’s losses at the polls in November. Obama won more than 70 percent of the vote among Latinos and Asians, and a growing number of GOP leaders believe that action on immigration is necessary to expand the party’s appeal to minority groups.

“Obviously, it’s had a very distinct impression,” said McCain, who lost his own bid for the White House in 2008. “It’s time to move forward on this.”

But, he added, “I don’t claim that it’s going to be easy.”

The accelerated pace signals that immigration reform is expected to be one of Congress’s highest priorities, and it comes as the White House prepares to launch its own public campaign on the issue.

Obama will travel to Las Vegas on Tuesday to speak about the need to “fix the broken immigration system this year,” the administration announced Friday. Nevada has a rapidly growing number of Hispanic voters, who overwhelmingly supported Obama’s reelection.

Obama also met with members of the Congressional Hispanic Caucus on Friday, and aides said he vowed that immigration reform will be his “top priority.”

“What has been absent in the time [since] he put principles forward is a willingness by Republicans to move forward with comprehensive immigration reform,” White House press secretary Jay Carney said Friday. “He hopes that dynamic has changed and there are indications what was once a bipartisan effort to push forward . . . will again be a bipartisan effort to do so.”

Past efforts begun amid similarly high hopes have sputtered.

In 2007, a bill crafted in the Senate died after failing to win support of 60 members despite backing from President George W. Bush. Many Republicans, and some centrist Democrats, opposed that effort because it offered a path to citizenship for illegal immigrants.

In 2010, extended negotiations between Graham and Schumer broke down without producing legislation.

The timetable would aim for a bill to be written by March or April and potentially considered for final passage in the Senate as early as the summer. Proponents think a strong bipartisan vote in the Senate would make it easier to win adoption in the GOP-held House.

The working group’s principles are expected to address stricter border control, better employer verification of workers’ immigration status, new visas for temporary agriculture workers and expanding the number of visas available for skilled engineers. They would also include a call to normalize the status of the nation’s 11 million illegal immigrants and help young people who were brought to the country illegally as children become citizens.

But obstacles abound. For instance, Rubio has said he thinks immigrants who came to the country illegally should be able to earn a work permit but should be required to seek citizenship through existing avenues after those who have come here legally.

Many Democrats and immigration advocates fear Rubio’s approach would result in wait-times stretching for decades, creating a class of permanent legal residents for whom the benefits of citizenship appear unattainable. They have pushed to create new pathways to citizenship specifically available to those who achieve legal residency as part of a reform effort.

It is not yet clear whether the Senate group will endorse a mechanism allowing such people to eventually become citizens — something Obama is expected to champion. Schumer said it would be “relatively detailed” but would not “get down into the weeds.”

A source close to Rubio said he joined the group in December at the request of other members only after they agreed their effort would line up with his own principles for reform. As a possible 2016 presidential contender widely trusted on the right, Rubio could be key to moving the bipartisan effort.

Rubio and other Republicans have said they would prefer to split up a comprehensive immigration proposal into smaller bills that would be voted on separately, but the White House will pursue comprehensive legislation that seeks to reform the process in a single bill.

“I doubt if there will be a macro, comprehensive bill,” said Sen. Johnny Isakson (R-Ga.), who supported the 2007 effort. “Anytime a bill’s more than 500 pages, people start getting suspicious. If it’s 2,000 pages, they go berserk.”

But Schumer said Friday that a single package will be key for passage. “We’ll not get it done in pieces,” he said. “Every time you do a piece, everyone says what about my piece, and you get more people opposing it.”

Eliseo Medina, secretary treasurer of the Service Employees International Union, which spent millions recruiting Hispanic voters last year, said immigration advocates expect Obama to be out front on the issue.

“The president needs to lead and then the Republicans have a choice,” Medina said. “The best way to share the credit is for them to step up and engage and act together with the president.”