CAPE CANAVERAL, Fla. — Astronauts inside and out worked to install a porch for experiments on Japan's expansive space station lab yesterday, a major objective made all the more difficult by microphone static that often drowned out the spacewalkers' voices.

Veteran spaceman David Wolf and rookie Timothy Kopra could barely make themselves understood at times because of the loud static emanating from their helmet microphones.

"Dave, you're unreadable," astronaut Christopher Cassidy called from inside the shuttle-station complex.

Two hours later, it was no better. "It's hard to follow along with this comm," Cassidy said, looking for clarification on what the spacewalkers were doing. The trouble lasted the entire 5 1/2-hour spacewalk, the first of five planned during Endeavour's space station visit.

NASA officials said it was a nuisance but not a safety issue, and they hoped to resolve the problem before the next spacewalk tomorrow.

With Apollo 11 on the minds of many back on Earth, NASA noted that yesterday's spacewalk was the 201st by Americans since those first steps on the moon by Neil Armstrong and Buzz Aldrin 40 years ago tomorrow.

Yesterday, Wolf and Kopra wasted no time 220 miles up prepping the Kibo lab — "hope" in Japanese — and the new porch for their mechanical hookup. Wolf removed an insulating cover from the lab and tossed it overboard; the white cover drifted away, flipping end over end.

The spacewalkers then moved on to other routine work at the international space station as their colleagues inside used the shuttle and station robot arms, one at a time, to lift the Japanese porch from Endeavour's payload bay and hoist it ever closer to the Kibo lab.

Once installed, the porch will mark the completion of Japan's $1 billion lab, so big that it required three shuttle flights to launch everything. The first two sections of the lab flew up last year.

The veranda — about 16 feet square — will get its first experiments in five more days.

Mission Control's congratulations to Wolf and Kopra, as they headed back inside, could hardly be heard because of the static. In the end, the two fell behind and had to skip some chores. They managed to free a platform for spare parts that jammed months ago, using a specially designed tool. But they did not have time to release a similar platform on the opposite side of the outpost.

Remaining inside the linked shuttle and station were 11 astronauts, a full house. The station population swelled to a record 13 when Endeavour arrived Friday for a 1 1/2-week stay. Kopra, the station's newest resident, will remain on board for another 1 1/2 months.