President Obama began three days of meetings on Capitol Hill on Tuesday by fielding about a dozen questions from Senate Democrats about ongoing budget negotiations, an immigration overhaul and his administration’s unmanned aerial drone program.

During the 90-minute exchange, Obama also heard objections from more liberal senators regarding potential cuts to entitlement programs as part of a bipartisan compromise on taxes and spending, according to senators in attendance.

Sen. Benjamin Cardin (D-Md.), a member of the liberal wing of the caucus, said the nearly 90-minute meeting, which Majority Leader Harry M. Reid (D-Nev.) tried to speed along, went over its allotted time.

"Sen. Reid gave [Obama] ample opportunity to leave and he decided to stay and answer more questions, so he obviously wanted to be there," Cardin recalled.

Without specifically addressing the timing, the president signaled his expectation of a months-long battle on fiscal issues that begins through the "regular order" of the House passing its GOP-drafted budget proposal and the Senate its Democrat-drafted one, the Maryland Democrat said. That process, according to senior congressional and White House aides, is likely to set up a long negotiation that could last into the summer as the debt ceiling approaches, possibly serving as the next back-stop to trying to force a so-called grand bargain of tax hikes and entitlement cuts.

"The best course now is to let the budgets go, get them into conference and try to reconcile the two," Cardin said of the president's views.

“He had a very upbeat message,” Sen. Carl Levin (D-Mich.) said of Obama. “He thinks it’s very important that we solve these problems together and he said that working together with Republicans in terms of getting a grand bargain or a major dent in this issue is critically important. But compromise is essential and he hasn't seen enough of it from them, but he’s also going to continue trying.”

Sen. Patty Murray (D-Wash.), who briefed Democrats on a budget she will release Wednesday before Obama arrived at the closed door meeting, said the president was encouraging about the direction of her spending blueprint.

"He was very supportive of the path we're on with our budget, encouraging us to get a budget out and work together," she said. "He was very supportive of the way we're heading."

Sen. Tom Harkin (D-Iowa), the most outspoken liberal critic of Obama's New Year's Day tax deal with Republicans, said that Obama gave his former colleagues reassurances on several upcoming issues. Unlike the prolonged talks in summer 2011, Obama said there would be "no negotiations on the debt ceiling" later this year when the Treasury runs out of its borrowing authority, Harkin said.

Additionally, Obama reiterated support for a larger debt deal that would include new tax revenue but also some cuts to entitlements that liberals such as Harkin opposed. The president, however, assured Democrats that his position would not move "any farther to the right", according to Harkin, suggesting that there would be no entitlement reforms unless Republicans agreed to substantial additional tax revenue.

In that vein, Harkin said that he and other liberals, including Sen. Bernie Sanders (I-Vt.), warned Obama not to cede ground on entitlement program spending, saying they hoped that the president would work to protect Social Security and Medicare, as part of a larger bipartisan bargain on tax and spending issues.

“He just said that he hopes that we can reach some kind of grand bargain,” Harkin said. “Some of us replied by saying, ‘Yes, but what’s in that grand bargain?’ We don’t want to start whacking away at Social Security or Medicare and things like that, which we have pathways to get out of this on without putting it in some kind of grand bargain that pulls the rug out from under our elderly, our sick. So we’re cautioning about that kind of grand bargain.”

On immigration, Sen. Chuck Schumer (D-N.Y.) said the president is "optimistic" about the Senate's work on the issue. Schumer is one of eight senators negotiating a comprehensive immigration overhaul bill.

Harkin and Levin confirmed that Obama fielded questions on his drone policy, but they declined to identify which senators raised concerns. The president vowed to continue sharing relevant information with members of the Senate Intelligence Committee, Harkin recalled.

Asked whether Obama’s lunches this week on Capitol Hill help lift the spirits lawmakers as they work on a host of complicated issues, Levin said, “Well, the food is always better, number one. Just kidding. The food is the same as it always is. It’s always great, whether you’re a Democrat or Republican, I hope it’s always great to see the president.”

Rosalind S. Helderman contributed to this report.