Driving up Massachusetts Avenue from Union Station to the new Convention Center is never going to be the same again. After reading the "D.C. Major League Park Site Evaluation Project," my heart and imagination will dance during every block of that trip.

In my mind's eye, I'll see a new 41,000-seat park with home plate 200 yards north of the intersection of Massachusetts and New Jersey avenues. The domes of the U.S. Capitol and Library of Congress, as well as Union Station, just four blocks away, would be framed beyond the right field fence. What a fantasy!

Or, two blocks west, closer to the Convention Center, imagine the same park -- with the right field wall flush against the north side of Mass Avenue. You'd have the same monumental outfield panoramas, but now you'd be so close to Chinatown, MCI Center and the Convention Center that Tiger Woods could stand on the pitcher's mound and hit any of them with his best drive.

After 31 years, somebody has finally spent the time and money to produce a quality study of the best available ballpark sites in the District and their potential costs. The two sites I've mentioned are my clear favorites out of five finalists in the evaluation project. But the other three are fascinating, too. The credit for commissioning this excellent work goes to the Mayor's office, the D.C. Sports and Entertainment Commission and the potential ownership group led by Fred Malek and James Kimsey.

Not long ago, the Northern Virginia's baseball group contributed a valuable study on the (relatively insignificant) impact on the Baltimore Orioles of a team in their region. Now, the Malek-Kimsey group has given us another essential piece of work.

At the World Series last month, everybody asked the same questions. "Where's the site for the new D.C. ballpark? How will it compare with other new parks? Is there one knockout location?"

From owners and general managers to the media, that's the first D.C. issue. Everybody understands this area's powerful demographics and our viable ownership groups. Everybody also knows that Orioles owner Peter Angelos may gum up the works.

Maybe we'll get a relocated team, the Expos or "other," in the next few years. Or not. That's unknowable. Here's what is certain. If you want a team, until you can talk ballpark specifics, you're just blowing smoke. Gorgeous (expensive) new parks drive the economics of the game everywhere. With the right plan, you're a player. Without it, don't waste your time. You're not a factor.

City governments, potential owners and taxpayers need to know exactly what they plan to build and where. How much of the financing will be public, how much private? And, considering that costs may be in the $400 million-plus range, the whole community needs to debate whether it even wants to build such a magnet park.

Just because Baltimore, Denver, Pittsburgh, Detroit, Chicago, Atlanta, Cleveland, Dallas, Phoenix, Milwaukee, Houston, San Francisco and Seattle have done it -- and, in most cases, are glad they did -- doesn't mean that Washington can or should.

What matters is that, finally, this serious and exciting discussion can begin. Now we have sites, talking points and guesstimates of costs for five possible D.C. sites. (Northern Virginia sites are a subject for the future, since no public determinations of sites have been made.)

Fans love nothing better than imagining the perfect park. Cozy, but not too small. A short walk from restaurants and entertainment. Near several Metro stops and major arteries from the suburbs. And, in this era when teams practically bring the Rocky Mountains or San Francisco Bay right into the ballpark experience, you'd want the symbols of Washington in play, too.

The first two sites mentioned have all of that. The three others have parts of it. And, in time, with commercial development, might have most of it. Now, whenever I'm at the intersection of New York Avenue and North Capitol Street, I'll imagine a third possible park. Look 100 yards to the southeast -- up toward Union Station and the dome of the Capitol. That would be home plate. Land there'd be cheaper with lots of commercial development potential.

When I take Interstate 295 over the Anacostia River into town, I'll look down and imagine a park right where South Capitol Street reaches the waterfront. No monuments in view, really. But esplanades, a tree-lined pedestrian mall and grand spaces would be available as a part of the Anacostia Waterfront Initiative.

Why, even when I go past RFK, I'll imagine a new park 400 yards north of the old one, with views over parkland to the Anacostia River only a 600-foot home run away. It's only inherent advantage? It might "only" cost about $340 million. All the others would be about $430 million. Except for the site closest to the new Convention Center, which might run $540 million because you'd need to buy, then demolish, some expensive buildings.

My initial impression is that the first site mentioned -- called "Capital North" at New Jersey Avenue -- would be fabulous. It's in the mid-price range. You could walk to the National Visitors Center, Shaw and Chinatown, all a half-dozen blocks away. You wouldn't have to create ambiance and entertainment. It's there. You'd expand the vibrant center of the city east by several blocks.

The second site, called "Mount Vernon Triangle," would be even better because you could practically touch all the "action" with a foul ball. Convention Center, MCI, Shaw and Chinatown: talk about synergy. But it's not $100 million better. Others got this prime real estate first. So, we should save it for our dreams.

The third site ("New York Avenue Metro") would work. But probably not nearly as well as the stunning Capital North, which should be far more visually appealing. The fourth site ("M Street Southeast") would have few land issues and, like New York Avenue Metro, would be a center for large-scale redevelopment with the consequent community benefits.

However, the Southeast site might lack the punch of the best new parks around the country. The first consideration, if you're going to commit to such a vast project, is that fans simply won't be able to resist coming to the park. That makes everything else work. That's why the fifth site -- RFK Stadium -- is simply a fallback.

This week baseball smacked Washington in the face again by deciding the Expos will play 22 games next season in San Juan, Puerto Rico, in ancient Hiram Bithorn Stadium, seating capacity 20,000 to 25,000 depending on what you count as a seat.

No doubt, baseball thinks it's laying the groundwork to dump on Washington, and protect the Orioles, again. But don't be so sure. San Juan may actually be the perfect foil for Washington.

Can San Juan consider building a $430 million park with the Capitol as a backdrop? Does it have ownership groups who look at annual operating costs in the $150- to $175-million range, then conclude, as the Malek-Kimsey site report does, that "there is far more than sufficient capacity to fund the baseball park project and support the operation of a successful franchise."

While San Juan is, perhaps, showing its limits as a big league town, Washington should be discussing whether, and where, it wants a new ballpark. And exactly how it would be financed.

If Washington decides to go this expensive route, now is the time to get hopping. By July, when baseball's relocation committee hopes to pick the Expos new home, we need to be able to say, "The day you give us a team, this is the park we can build."

Nothing is more likely to precipitate relocation than a plan for great new park. Inaction on the issue is tantamount to concession.