WASHINGTON — Lawmakers donned face masks. Congressional employees’ desks were ensconced in plexiglass shields. The floors and sidewalks of Capitol Hill were marked with circular panels emblazoned with images of feet to show lawmakers and aides where to stand to keep a safe social distance — like dance-step diagrams, but for trying to avert the transmission of a lethal virus.

With the Senate back in Washington for a session that Congress’s top doctor said carried health risks given the continued spread of the coronavirus, the chamber has quickly resumed a semblance of its routine, but with some trappings that cast an eerie pall on the proceedings.

Senators across the country traveled back to the Capitol in time for a confirmation vote on Monday afternoon, with one or two stragglers rushing to the floor in the jeans they wore on the plane. Hearings unfolded on Tuesday as usual — albeit in half-empty rooms, in line with new policies to avert the spread of the virus. Senator Mitch McConnell of Kentucky, the majority leader, readied yet another vote on a lifetime judicial appointment.

“Normal,” observed Senator James Lankford, Republican of Oklahoma, his deep drawl muffled slightly by a gray mask his wife made. “Except it’s not normal.”

Summoned back to Capitol Hill for the first time in 40 days, the Senate, an institution loath to change, found itself doing just that in the face of the pandemic. Though drastic measures were eschewed — a procedure for remote voting, for example, has not yet been established — lawmakers and their entourages took small steps to adjust their routines to accommodate the health precautions necessary to avoid the spread of the virus.

With many of their reliable direct flights to Washington canceled, several senators were forced to drive or add on layovers to reach the Capitol. Many directed all but one or two aides to work from home. The hallways — normally bustling on a Tuesday as senators huddle for party luncheons, reporters angle to question them about the latest developments and the machinery of the Senate grinds into full gear — were noticeably hushed.

Senator John Thune of South Dakota, the No. 2 Republican, and an aide rode the Senate subway in adjacent cars rather than together, staying far apart on a vehicle that is normally crammed with lawmakers, staff members and pages racing to reach the floor. Another aide paired his seersucker suit — a favorite warm-weather sartorial choice in the Senate — with black gloves and a mask, exuding a kind of Brooks Brothers meets the grim reaper look. Senator Kyrsten Sinema, Democrat of Arizona, cast her vote on Monday with a finger pointing to her $12.99 lavender wig.

“I think we’re all looking at one another going, this is weird, isn’t it?” said Senator Lisa Murkowski, Republican of Alaska, who has not returned to her state in nearly two months because of a strict quarantine requirement that could prevent her from traveling back to the Capitol to vote. “It’s good to get out and see a little change of scenery.”

Sparse attendance was mandated at hearings to ensure appropriate distance between senators. When the Intelligence Committee convened the Senate’s first hearing in a month, to question — from ample distance — President Trump’s nominee for director of national intelligence, senators came and went from the room in carefully coordinated waves to limit its occupancy. The hearing stopped promptly at noon to allow time for a deep disinfection before another panel met in the room on Tuesday afternoon.

The Banking Committee, meeting to consider the nomination of Brian D. Miller, the White House lawyer tapped to oversee the Treasury Department’s $500 billion coronavirus bailout, adopted a hybrid hearing system that allowed for senators to appear in person or over a livestream. Senator Sherrod Brown, Democrat of Ohio, questioned Mr. Miller from his home in Cleveland with his dogs barking in the background.

“I hope I’m not looking as yellow to the rest of my colleagues as I look on this screen to me — this is not a case of full-on jaundice yet,” said Senator Mark Warner, Democrat of Virginia, who indeed appeared yellowish over the video stream. “This looks pretty God-awful.”

So did the weekly Republican news conference, which usually unfolds in an ornate area just off the Senate floor known as the Ohio Clock Corridor, but on Tuesday took place in a bare basement meeting room where the glare of television lights cast looming shadows on the bright white walls. The party lunch was moved out of the stately but small, Vermont marble- and black walnut-paneled Mansfield Room in the Capitol to a larger space in a central hearing room tucked away in an office building nearby. Lunches were boxed, not served, and there were only three senators to every table, with a box of wipes and hand sanitizer on each.

Senate Democrats outright canceled their lunch and conducted it by phone.

Senator Rand Paul, Republican of Kentucky, the sole senator to have tested positive for the virus, was one of the few lawmakers this week walking around without a mask, assuring reporters on Tuesday that, “of all the people you’ll meet here, I’m about the only safe person in Washington.” (It remains unclear, health experts say, whether antibodies prevent another round of infection.)

But with nearly half of the senators over the age of 65, putting them at higher risk for infection, the pandemic has prompted an undercurrent of anxiety in a building unaccustomed to accommodating for personal space.

In the press galleries and cafeterias, plexiglass shields protected those sitting behind desks. And some of the inner chamber doors, typically closed, were flung open during Monday’s vote so handles could remain untouched, making it possible to see the presiding senator from the Capitol Hill rotunda more than 65 yards away.

“Here’s one for the records,” a Capitol Police officer said on Monday as he pulled out his iPhone to snap photos of the transformed Senate basement: red and white posters offered a stick figure interpretation of how to properly stay six feet apart, and large yellow dots on the floor that Capitol Hill employees had measured with a six-foot wooden pole just hours earlier marked where to stand.

Even with the House yet to return, the precautions extended across the Capitol to a swearing-in ceremony for Representative Kweisi Mfume, the Maryland Democrat newly elected to finish the term of Representative Elijah E. Cummings, who died in October.

As his wife, Tiffany Mfume, held the family Bible on Tuesday to pose for a photograph, a single strap of her surgical mask, removed for the occasion, could be seen underneath. Speaker Nancy Pelosi of California also placed her pale pink mask, which matched her pantsuit and glittering stiletto heels, on her neck while photos were taken.

The other Democrats in Maryland’s delegation were more torn about their face gear, debating what to do as Ms. Pelosi looked on. Representative Jaime Raskin kept his padded mask, featuring the state flag, securely fastened, while Representative Steny H. Hoyer, the majority leader, held his blue surgical mask by his side. Representative C.A. Dutch Ruppersberger at one point let his Baltimore Ravens mask dangle from one ear as camera shutters clicked away.

“I don’t know how I’m going to get to know everybody,” said Mr. Mfume, who is about to begin a second stint representing Baltimore in Congress nearly 25 years after giving up his seat. “It’s going to take a minute.”

Nicholas Fandos contributed reporting.