Keith Lockhart has turned 40 and Tuesday night he opens his fifth season with the Pops -- already he's conducted 300 concerts with the orchestra in Boston and on tour, recorded four chart-topping CDs, and made more than a dozen successful television programs.

''It's all a bit hard to believe,'' Lockhart confesses over lunch, sounding upbeat and not the least bit weary. On the contrary, the sunny conductor says, ''There's lots to look forward to, both change and continuity.''

Nearly everything about the new Pops season has already been announced -- early facts about the annual Fourth of July extravaganza on the Esplanade are once again notoriously hard to come by -- but Lockhart is willing and eager to fill in background and details. He himself will lead 36 concerts, tape four ''Evening at Pops'' TV shows (''Brush Up Your Shakespeare,'' ''Swingin' at the Pops,'' a tribute to Danny Kaye starring Nathan Lane, and a program featuring Broadway/crossover sensation Audra McDonald), and record his fifth Pops CD.

''This will be a Fourth of July album,'' Lockhart says, ''and it will be a very fast turnaround. We will record it three weeks into the season, finishing on the 24th of May -- and the release date is June 25, in time for the holiday. The Pops has this incredible association with holidays and with the Fourth of July in particular. While the Pops has made lots of patriotic albums, we've never done this. One of the featured attractions will be a famous overture with cannons and bells. We want to use our own, so the producer will be visiting the belfries of Boston. Of course we'll play 'The Stars and Stripes Forever,' and there will be a new choral harmonization of the national anthem. You have to be careful with the national anthem because people don't like new arrangements that call attention to themselves. Stravinsky found that out -- and so did Roseanne!''

Lockhart is particularly pleased by a new Pops commission that will appear on the album, ''With Voices Raised,'' which was written by the creators of ''Ragtime,'' Stephen Flaherty and Lynn Ahrens. ''What we wanted was something to add to the familiar voices of Thomas Paine and John Hancock and all the famous people of the past whose words have made their way into patriotic music. We wanted music for the voices of Americans in the 20th century. There are quotations from the women's suffrage movement, from the civil rights movement, from the gay rights movement. Some of the words are set into the choral texture and some appear in the narration, which comes in the voices of different famous Americans. We're hoping to get Whoopi Goldberg to be the voice of Sojourner Truth on the recording. Another nice thing will be a new arrangement of 'America the Beautiful' that Met mezzo-soprano Denyce Graves will sing with us; I wanted something something simple, soulful, and gorgeous, not a generic patriotic arrangement.''

Lockhart had spent the day before our interview in New York being photographed for the album. His album covers have been even more outrageous than the fearless Arthur Fiedler's were, but he volunteers no information on what he wore or did in the pictures. Under questioning, he does admit that he will not be seen sitting on an American flag -- in later copies of an earlier Lockhart/Pops record, ''American Dreams,'' RCA/BMG replaced the photo of Lockhart sitting on a corner of the flag that proved controversial.

A large part of the Pops's new-arrangement budget this season went to ''With Voices Raised.'' Most of the rest went to some new arrangements of Duke Ellington material. ''This is the Duke Ellington centennial, and the Pops has every reason to be proud that Arthur Fiedler invited him to perform and record with the Pops when that was still a pretty daring step to take. Now the Boston Symphony is going to be looking into some of the works Ellington wrote for orchestra. It's funny, how these things go in circles. ''Next year brings the centennials of Copland and Kurt Weill -- 2001, I am happy to report, doesn't contain any major anniversaries, but I am hoping that we will have a new piece by Christopher Rouse for that season. I talked with him about it at Tanglewood, and he seemed delighted by the idea -- after all, in one of his composer-residencies, he made an orchestral arrangement of 'Twist and Shout.' ''

Lockhart says the Pops is close to announcing the appointment of its first full-time manager. At the top of his personal wish-list for the organization would be ''more opportunities to break out of the tyranny of the schedule'' -- a sentiment that was shared by Fiedler and by John Williams before him. ''No one wants to tamper with the formula that has been so successful for so long, but it would be nice to be able to have a couple of 'Pops-on-the-edge' events every season that didn't fit the mold -- and that might help bring in different audiences.''

Lockhart takes a moment to pay tribute to the season's other conductors, John Williams, of course, at the head of the list. Williams, now conductor laureate, will return for 10 concerts, as well as a television taping with Itzhak Perlman, Dawn Upshaw, and Vic Damone. Williams and the Pops will also record a CD with Perlman. Williams's programs, naturally, will include the first live performances of music from his new score to ''Episode I -- The Phantom Menace.''

Harry Ellis Dickson, Pops associate conductor laureate, celebrates his 90th birthday this year; he'll be back for ''Old Timer's Night'' and for the annual Arthur Fiedler Memorial Concert on the Esplanade July 6. Returning guest conductors include Charles Floyd (the popular ''Gospel Night'' is June 27 with the great Boston Pops Gospel Choir and baritone Jubilant Sykes), Mitch Miller, Bruce Hangen, Richard Hayman (a Pops arranger for more than four decades, making his first local podium appearance in years), and James Orent, a member of the Esplanade Orchestra, the regular stand-by conductor whose scheduled appearances have pleased audiences. There will be one debut: Jeff Tyzik, principal Pops conductor of the Rochester Philharmonic since 1993.

This has been a big season in Lockhart's life outside the Pops. He bade farewell to the music directorship of the Cincinnati Pops in a concert including the Barber Violin Concerto, which featured his wife, Lucia Lin, as soloist. This was their first conductor/soloist collaboration, though Lockhart has been playing piano in occasional chamber-music concerts with his wife. ''She was really great,'' Lockhart says with pride. ''And I'm not saying that just because I'm married to her.''

This season Lockhart took over the music directorship of the Utah Symphony from Joseph Silverstein, former concertmaster of the Boston Symphony. ''This year every scrap of time I had saved for myself went to Utah -- even my laundry days! Our house in Salt Lake City is still largely empty, devoid of furniture, but at least we have a house now -- and it's right down the street from the Silversteins, which I didn't realize when we bought it. So far things seem to be going very well. The string players know how to play in an orchestra, as you can imagine.''

Lockhart was especially pleased by concert performances of ''Porgy and Bess'' that he conducted in Salt Lake City, and he has big plans for the future, including the Utah premiere of Britten's ''War Requiem'' next season. Pianist Emanuel Ax will be the gala opening-night soloist, playing Beethoven's ''Emperor'' Concerto. ''I saw Manny walking along at Tanglewood, wearing shorts, so I leaned out the window of my car and asked him if he'd come to play something with us in Utah and he called back, 'Sure!' ''

Lockhart also had a busy season as a guest conductor; he has become a particular favorite in Montreal. He's also worked on the pilot for a television project he's not free to announce yet, but it will be a program for children. ''For the pilot, we licensed Pops recordings, but the actual programs will feature the Pops and me, along with animated characters.'' Lockhart wasn't able to capitalize on the success of his operatic debut with ''The Ballad of Baby Doe'' in Washington, D.C., last season, because there wasn't time enough in his schedule, but that's something he would like to do.

And he would like to see more of his wife, who has had a busy year of her own, what with her position in the Boston Symphony, her solo engagements, her work with the Boston Trio, and her new job as the second violinist in the Muir Quartet. ''The Muir is one of those unusual quartets where the players actually like each other -- Lucy has known the first violinist, Peter Zazofsky, since they were in the Wieniawski Competition in 1977, when they were both kids. Right now it's great that I am going to be at the same address for three months. The only problem is that Lucy is going to be in Japan and China with the BSO for the first three weeks of it!''