What a difference a letter makes.

Lexus manufactures two sport-utility vehicles with very similar names — the GX 470 and the LX 470 — but considering that getting an “L” instead of a “G” costs nearly an extra $20,000, it’s a good idea to know exactly what you want before writing that check at the dealership.

Having tested both SUVs with full-time four-wheel drive, I can tell you that the mechanical differences between the two are not that great. Luxury-and amenities-wise, it’s another ballgame.

To put it in Monopoly board-game terms, the GX 470 is Pennsylvania Avenue, and the LX 470 is Boardwalk.

For those who have never played Monopoly, let’s take it a step at a time and start with the new-for-2003 GX 470. It’s a big step up from the entry-level Lexus SUV — the RX 300, soon to become the RX 330.

Sweetly styled with smooth lines, fender flares and swept-back, integrated headlamps, the GX 470 oozes Lexus-level class. The story was the same inside the tested model — leather to the max with a nice blend of maple wood trim all about, including the steering wheel.

Standard seating in the GX 470 is five, but a third row can be added to accommodate three more passengers. Personally, if I had my eye on the vehicle, I’d stick with the five-seat arrangement and use the back for transporting cargo alone. I had the optional third-row seat — with a back-bench air conditioner also thrown in — and it would be a tight squeeze for three adults.

Rolling, the GX 470 was most impressive. The 4.7-liter V-8 with a robust 235 horsepower and an even more impressive maximum torque rating of a 320 foot-pounds dug in and effortlessly zipped the vehicle ahead of traffic accelerating from stoplights (80 percent of the torque kicks in at a mere 1,100 revolutions per minute). Merging onto local freeways was a breeze.

Even when working hard, the GX 470 showed little strain. The SUV went about its work quietly, and a rock-solid suspension kept the ride smooth. Special features controlling ride height and the damping rate of shock absorbers undoubtedly contributed to the silky feel.

Those cavalier enough to take a vehicle with a starting price of nearly $45,000 off-road will find that chore made easier with the GX 470’s “Downhill Assist Control,” which automatically holds the SUV to a low target speed during steep descents.

A fuel-saver the GX 470 is not. The federal ratings are 15 miles per gallon in city driving and 18 mpg on the highway. My own monitoring came in about 1 mpg less on both counts.

All in all, however, the GX 470 is a formidable middle-range luxury offering, certainly a competitor against other SUVs in the $40,000-plus segment.

Naturally, there are those who want more, and for them there is the LX 470. My tester started at $63,125 and had a bottom line of $66,703. For these prices, a vehicle should have a lot — and the LX 470 does.

The tested LX 470 came with the same engine and four-wheel-drive system as the GX 470, and many of the handling enhancements on the two vehicles were identical. The LX 470 is not even that much bigger than the GX 470 (although three people in the third-row seat have more room to spread out in the LX 470).

But the LX 470 justified its pricing with a host of comfort, convenience and luxury features befitting the top-of-the-line SUV in the Lexus fleet. The list of goodies included a standard DVD-based navigation system, power-folding exterior mirrors and dual-zone climate control with smog-sensing technology.

The tested LX 470 also came with a $2,200 option called the “Night View System,” the greatest night-driving feature since the invention of the headlight and the best two-grand-plus you can spend for a little safety and security. Yes, similar systems have been on the market — Cadillac has touted its worthy offering for years — but the new Lexus system is state of the art.

The system projects near-infrared beams from two lamps built into the front bumper. The light reflects back to what Lexus calls a “Charged Coupled Device camera” mounted inside the SUV, at the top of the windshield. There, a computer processes images that are then projected onto the lower section of the windshield, just under the driver’s normal field of vision.

In contrast to infrared systems that detect sources of heat but blur surrounding objects, the Lexus system projects basically a clear, black-and-white television picture of everything nearly 500 feet ahead of the vehicle — including trees, boulders and road edges. During a late-night run from Lake Tahoe to Sacramento on Highway 50, I was able to clearly see sharp curves and various woodland features way before my eyes could see them.

Simply put, NVS is an enormous safety aid. It truly could be a lifesaver.

Grumbles on the LX 470? Well, it pains to see fuel-economy ratings of 13 mpg in the city and 17 mpg on the highway. A typical driver is likely to pay more than $1,600 a year for gasoline; a busy traveler is going to spend enough in a year to buy that Night Vision System.

The LX 470 tips the scales at about 1,000 pounds more than the GX 470, which means that the 4.7-liter V-8 has to work much harder to move the former. From a standing start, the GX 470 is much more satisfying in the performance department.

All things considered, it boils down to choice. As for me, I’d probably take the GX 470 as a vehicle that gives me plenty of what I need on the roadways. My guess is that many dedicated SUV drivers looking to move up in class will feel the same way.

If you want the whole Lexus experience and are fortunate enough to have the financial juice to swing it, the LX 470 should absolutely please you.

Whatever the choice, Lexus’ SUV lineup is now more loaded than ever.