This is one of my favorite scenarios. It's a great way to introduce newbies to SFB: you give the Fed to an experienced player and get three noobs to play the Klingons. They still win, but have to learn to work as a team in order not to lose a ship or two.
To answer your question, planetary protection doesn't help enough to save you. About the only thing the planet actually does is allow you to evade drones targetted on you. This can be a big help against a scatterpack shuttle. Honestly, outgunned 3-1 the Klingons have an easy job, planet or no planet. The biggest question is whether or not they will lose a ship.
The ideal Klingon tactic goes something like this: you have 1 cruiser put everything into speed so that he can reach the Hood ASAP. Remaining power goes into tractors. The Klingon either tractors the Hood or the Hood blows lots of power fighting it off. The second cruiser loads his disrupters to standard loads and takes a potshot with them when he gets as close as possible. He can convert to overload with batteries if he gets close enough. The goal of this ship is to do shield damage so the Hood has a weak shield to protect. The third ship (the D7) overloads his disrupters as much as possible making sure he can get in range to use them if the first ship wins the tractor battle.
Then the Klingons pound the weak shield on turn 2 and if they don't blow the Hood up then, they send marines over to attempt to capture it. If the Hood manages to survive turn 2, it won't survive turn 3.
There are three Federation strategies that I've seen. Strategy 1 is to get behind the planet and load all your weapons so you can at least take one of them with you. If all the OL photons hit, you might get lucky enough to take two of them with you. Strategy 2 is the shortest version. You charge the Klingons and hope they do enough damage to your warp engines that you can disengage on turn 2. If it works, you live and win a heck of a strategic victory. No matter what the case, you try to separate the saucer if things don't go well (and they usually won't).
Now for version three, trying to win with the Hood. This is the only way to become a Legendary Captain. First, the Klingons have to employ the strategy outlined above. When the first Klingon reaches you, you let it tractor you and don't fight it. You face it and blast its shields down at point blank range with all your phasers. Then you beam marines over. You will take some damage from Klingon #2. If you take only a little, you can win. On turn 2, you use OL photons to savage Klingon #2. If you hit with at least three, you can win. You beam over more marines to Klingon #1 and hope they can win the battle for that ship before Klingon #3 beams marines over to help them. If you don't think you can win that way, have the marines do hit and run raids on both turns one and two against the security stations of ship #1. If the crew revolts, you're in good shape. Finally, if things have worked out ideally, you have your ship and a captured Klingon against a single Klingon. You can win that. If you had to do the H&R raids you're in good shape to disengage having destroyed ship #2. So, if everything worked perfectly, you blow up ship #2, ship #3 disengages, and you capture ship #1.
I've played this scenario many times as the Federation. Usually you get your butt kicked. I've never succeeded at strategy #1 (mostly because your goal is to go down fighting - you always die in that variant). Strategy #2 sometimes, but not usually, works.. AFAIK, strategy #3 is my own design. I've won with it but only because Klingon #3 didn't think to beam marines over to help Klingon #1 AND I got extremely lucky..