The first true space colony completes its mission and returns to Earth this morning--without a single human in residence. An extended family of carpenter ants from Camden, N.J., beat all of mankind to the punch.

About 20 of the high school students and recent graduates who put these now-famous insects aboard the space shuttle Challenger visited Capitol Hill yesterday to explain to curious legislators why NASA agreed to ferry a classroom science project alongside classified Air Force experiments and international communications satellites.

"We are hoping to see how the ants, which are very social insects, adapt to living in a weightless environment," student Anthony Trusty told Rep. Bill Green (R-N.Y.) during a bustling cocktail hour in the Rayburn Building sponsored by the House Space Caucus.

"But will they have enough food?" Green wanted to know. "Yeah, plenty," Trusty replied, launching into a brief lecture on ant nutrition.

Rep. James Florio (D-N.J.) was even more baffled. "Is it an animal?" he asked an aide, who seemed equally puzzled. "Sure it is," the congressman concluded on his own. "Okay, we'll make the ant the official animal of Camden."

Many in attendance, including students, teachers and NASA administrators, wore "I Love Ants" buttons.

Dubbed Orbit '81 because the ants were originally supposed to take off two years ago, the project emerged from a science enrichment curriculum for minority students introduced in 1978 at Camden and Woodrow Wilson high schools, both located in the hard-pressed industrial city. RCA, Camden's largest employer, put up $10,000 for a tiny space shuttle condo, which the students leased through NASA's "Getaway Special" program. The space agency routinely rents out leftover compartments in the shuttle's cargo bay for small experimental payloads.

"The ants have the closest social structure among insects to that of humans," explained Andre Nieves, who graduated last week from Woodrow Wilson. "The big idea is to look toward human colonies and see what we can learn to prepare for them."

One hundred and fifty of the six-legged pioneers traveled at 17,500 mph in a specially built ant farm placed in a canister about the size of a trash can. The Camden students positioned video cameras inside the canister and programmed a microcomputer to supervise the filming of ant activities in outer space.

It was a real team effort. Shop classes produced the hardware, journalism classes provided the public relations, art classes decorated school hallways with imaginative space murals. Forty of the students attended the Challenger's launch at Cape Canaveral, and two will go this weekend to retrieve equipment.

But what if the brave ant astronauts turn up dead? "We know from tests they can stand the heat, that they have enough food, that they can stand the vibrations," said Joe Rolen, a 1980 Woodrow Wilson grad studying chemical engineering at Drexel University. "Ants are tough; that's why we picked them after a lot of research."

Regardless of what health the ants are in when they touch down this morning, the Camden program has been a clear success.

"It motivated all of us to work together, to look more into the science fields," explained Julie Rivera, a junior planning to study computer science in college. "The astronauts seem to be having a real nice time," Rivera observed matter-of-factly. "It's a dream, but I wouldn't mind working for NASA."

Said fellow student John Wilson: Orbit '81 "showed that students that come from a rundown area aren't always deprived academically . . . We can compete."