Bipartisan immigration legislation being written in the Senate would require surveillance of 100 percent of the U.S. border with Mexico and apprehension of 90 percent of people trying to cross the border in certain high-risk areas, a person familiar with the proposals said Wednesday.

People living here illegally could begin to get green cards in 10 years, but only if a new southern border security plan is in place, employers have adopted mandatory electronic verification of their workers’ legal status, and a new electronic exit system is operating at airports and seaports.

The person provided the information on condition of anonymity because the deliberations were private.

The contours of the tough new border security plans emerged as senators moved closer to unveiling sweeping legislation within days that would put about 11 million immigrants living here illegally on a path to citizenship and allow tens of thousands of high- and low-skilled workers into the country on new visa programs, in addition to securing the border.

Lawmakers and aides said all the major elements were complete, or close to being complete. A final deal was pending on a new visa for agriculture workers, and there were small details to be dealt with on visas for high-tech workers, but Sen. Dick Durbin, D-Ill., said it wasn’t enough to hold up the bill.

“We are closer now than we have been in 25 years for serious immigration reform,” Durbin said Wednesday after he and other Democrats in the Senate negotiating group briefed members of the Congressional Hispanic Caucus. “This president is behind it, and there is a strong, growing bipartisan effort in the Senate to support it. We hope that the House will do the same.”

Meanwhile, tens of thousands of pro-immigration activists gathered outside the Capitol and in cities around the country to push Congress to act. They waved American flags and carried signs reading, “Reform immigration for America now!”

The border security piece of the legislation is critical to getting support from Republicans, but some Democrats have opposed making a path to citizenship contingent on border security. Sen. Chuck Schumer, D-N.Y., said the new requirements wouldn’t impede citizenship.

“A lot of people here would not want to put dollars into the border, but as a price to get citizenship — as long as it’s not an impediment to citizenship but rather works alongside citizenship — it’s something we can all live with,” Schumer said, after talking to the Hispanic House members. “What we’ve said all along is, triggers have to be objective and attainable in a way it doesn’t interfere or delay with people becoming citizens, and that’s in the bill.”

The goals would be achieved by giving the Department of Homeland Security six months from the bill’s enactment to create the new border security plan deploying the personnel, infrastructure and technology needed to achieve the 90 percent effectiveness rate. Also within six months, the department would have to create a plan to identify where new fencing is needed on the border. Once those plans are certified, people living here illegally could begin to apply for a provisional status allowing them to work here legally.

After 10 years, people granted “registered provisional immigrant status” could apply for green cards granting them permanent residency — and the ability to seek citizenship — if the new security and fencing plans have been completed, the mandatory employment verification system is in place and used by all employers, and the new electronic exit system is operating at airports and seaports, collecting machine-readable visa or passport information from airplanes and ships.