Architect Peter Chermayeff was 38 when he got a phone call about the possibility of designing an aquarium for Baltimore's waterfront.

Housing commissioner Robert C. Embry Jr. had visited Boston's popular New England Aquarium, which opened in 1969, and envisioned building a similar attraction for Baltimore's Inner Harbor. Aware that Chermayeff led the design effort for New England, Embry wanted to hire him for Baltimore as well. It was an enormous responsibility for such a relatively young architect, but Embry didn't consider it a gamble.

Chermayeff was a "very strong designer" with a good reputation for working in an urban context, Embry recalled recently. Plus, he already had designed one aquarium for a waterfront setting similar to Baltimore's. "It seems to me that it would have been a gamble to go with anyone else."

Embry's overture to Chermayeff led to the creation of the National Aquarium in Baltimore, the seven-story aquatic museum that recently celebrated its 20th anniversary. Besides forming the sculptural centerpiece of Baltimore's Inner Harbor, it's one of the most successful aquariums in the United States, drawing 30 million visitors since its opening and setting off a wave of aquarium construction around the world.

Now Chermayeff is back for an encore. With longtime partners Bobby Poole and Peter Sollogub, he's designing a $48 million addition to the Pier 3 building, a glass-enclosed structure that will extend the aquarium's global reach and give visitors new reasons to return. But this time he is no neophyte at aquarium design.

Since Baltimore's aquarium made its debut, the Massachusetts-based architect has become an international leader in aquarium design, with six major projects open and many others on the drawing board. Besides Boston and Baltimore, he has completed aquariums in Chattanooga, Tenn.; Osaka, Japan; Lisbon, Portugal; and, in collaboration with Italian architect Renzo Piano, Genoa, Italy. He is working on aquariums for Virginia Beach, Va.; Islip, N.Y.; New Bedford, Mass.; Hartford, Conn.; Coralville, Iowa; Homestead, Fla.; and Shanghai, China.

In 1998, Chermayeff left the firm he helped start in 1962, Cambridge Seven Associates, and established a new office that specializes in aquarium design -- one of the only companies in the world that does so. Its name is Chermayeff, Sollogub and Poole Inc., or CSP, and all three name partners played key roles in the design of the National Aquarium.

For the past 11 years, Chermayeff also has been president of a second firm, International Design for the Environment Associates Inc., or IDEA. It's a company devoted to the design, development, construction and operation of aquariums and other "nature related attractions."

After creating buildings for others over the past four decades, Chermayeff is now working to fulfill perhaps his most ambitious goal yet. He wants to own an aquarium -- one that he designed, filled with creatures and operates. After exploring numerous locations over the past decade, he finally may get a chance to do that in Dusseldorf, Germany.

Chermayeff's plans cross the traditional lines that separate architect, builder and client, and may lead to conflicts with some of the institutions with which he already works. That's an unavoidable byproduct of the stature he has attained since accepting the challenge to design Baltimore's aquarium -- and his desire to accomplish even more.

"Most architects would consider themselves fortunate to have completed one major public building in their lives," he observed during a recent visit to Baltimore. "We've been fortunate to have eight or more, with others to come."

In town to attend the aquarium's anniversary celebration, and looking not much different than he did the day it opened, Chermayeff said he'll always be grateful for the early support he received from Embry and then-Mayor William Donald Schaefer.

Even more than the New England Aquarium, he said, Baltimore's project propelled him on a career in aquarium design because he learned so much from his work here and so many key decision-makers wanted to replicate it in their cities.

Chermayeff says he's especially pleased to have been invited to work on projects such as the Lisbon Aquarium, a key attraction of the 1998 World's Fair in Portugal.

"When the leaders of another country and another culture want me and my colleagues from America to design a building that will be the centerpiece of their exposition," he said, "it's a great honor."

From tadpoles to aquariums

Now 65, the father of two, Chermayeff is the quintessential Boston Brahmin, in hand-tailored suits and round spectacles. Erect, proper, unfailingly polite, he has a trace of a British accent when he speaks, which is always eloquently and with great conviction. But there was a time when he wasn't sure he would practice architecture at all, much less specialize in aquariums.

The chief designer of Baltimore's aquarium was born in London in 1936, the son of Russian-born architect and educator Serge Chermayeff. He emigrated to America with his family during World War II, attended Phillips Academy in Andover, Mass., and studied architecture at Harvard University, where his father taught the same subject.

The young Chermayeff was exposed to nature and the world of water in a variety of ways. As a boy, he spent summers collecting tadpoles and newts on Cape Cod, where his family had a vacation home. While at Phillips, he spent many weekends with his "second family," architect Walter Gropius and his wife, both serious birdwatchers.