Lawrence E. Walsh, independent counsel of the Iran-contra affair, is a 75-year-old man of considerable gravity, focus and grasp.

From the press he has received since he came to town, you might have thought otherwise. Members of congressional committees also investigating the matter have expressed considerable dismay with him, muttered that he was, if not over the hill, well, a little out of touch, and taking too much time chasing "grand, wild conspiracy theories."

This week Walsh came under new fire from the Justice Department for spending too much money. Walsh's 13th Street offices at the grand new I.M. Pei building rent for $32 a square foot, according to Assistant Attorney General John R. Bolton, who complained bitterly about Walsh's New York lawyer "life style."

Walsh has remained quiet through it all. He came to town with a reputation as a tough, thorough, big time, big-case Republican lawyer, and a former federal judge. Disillusion set in almost immediately on Capitol Hill, which groaned at his tortoise pace and his inability to understand the lawmakers' pledge to meet an August deadline for the hearings' windup. "Aloof, patrician," they complained. "Decent, honorable," they conceded.

So it is almost surprising to meet Walsh in the austere conference room of his headquarters and to see -- far from a dodderer -- a magisterial presence with a long, rosy-cheeked face, an attentive manner and such a stickler that he will not comment on the legality of the Boland Amendment. But he is perfectly willing to explain in detail why the scandal-probers are so expensively quartered.

"We would have loved to be in the courthouse or another government building. We also looked in the Watergate office building and in another building on Connecticut Avenue, but they would have required structural changes to meet the security requirements that would not have been feasible."

Of Bolton's press conference -- "intemperate" even the White House allowed -- Walsh observed dryly, "I was somewhat surprised by the content -- and the tone."

"My life style has never been as good as when I was in the Justice Department, doing civil rights cases {during the Eisenhower years}. I had a huge office. Our entire office space here would fit into the personal suite of the attorney general. Mr. Bolton is in for a rude shock if he sees it."

He thinks his differences with the congressional committees are lessening. They clashed over granting immunity to the principal witnesses, Rear Adm. John M. Poindexter and Lt. Col. Oliver L. North. He sees it as inevitable conflict between politicians who want to get a story out fast and prosecutors who wish to build criminal cases that will stand up in court.

"They have to finish their work as quickly as possible for it to be useful to Congress and the public. We take the time to develop peripheral and minor witnesses."

His first request was for no immunity at all for North. Refused. Walsh asked for 90 days' delay. Granted. Then he asked them to wait and see if their questioning of Poindexter would make North's testimony "duplicative or unnecessary." The committees voted to hear North next month.

Actually, Walsh's life style has been as austere as his offices -- where there are only two pictures, both on loan. He lives at the Watergate, where he stayed "long before I got this job," works 10 hours a day and has been out exactly three times, at the Gridiron, and two correspondents associations' dinners. He leaves Friday for his home in Oklahoma City to join his wife and the swimming pool in his back yard.

He sets the agenda every Tuesday for the 25 attorneys, divided into four teams by subject and witness, on his staff. A separate unit of 35 G-men works in the FBI basement. One team operates out of New York on legal questions. Another handles motions, matters like the challenge to the constitutionality of the independent counsel law recently brought by North.

How does a lifelong Republican, who began his career as an assistant to Thomas E. Dewey, a lawyer he greatly admired, feel about investigating a scandal that could do his party irreparable harm?

"I don't think the exposure to truth is bad, really, for anyone. The premise of democracy is that the truth is known or is ultimately knowable. The electorate functions on the basis of knowledge and a resolution of the facts."

Before he was offered his momentous job, "I considered whether I would accept it if it came." But once he was asked, he had no reservations.

"I love a challenge," he says. "And the importance of it makes it an honor."