Here's a few ideas for a core only martial cleric:
ABILITY SCORES:
STR - 14 (6) - Most efficient way to get decent STR; you have lots of buffs for this
DEX - 12 (4) - Maximize AC in full plate
CON - 14 (6) - HP are always good for a tank
INT - 10 (2) - You have some good skills but this is a dump stat
WIS - 15 (8) - Drop your level up stat boosts here and you'll be fine. Cleric tanks self-buff so high DCs are not needed
CHA - 14 (6) - Fuels Divine Might as well as helps Turn Undead and some nice skills
If Divine Might is not allowed, I'd drop CHA down to 10 and boost STR to 16.
SPELLS:
Your key buff spells are Divine Favor (I), Divine Power (IV), Righteous Might (V), and Quickened Divine Favor (V)
TURNING:
Turn Undead is quite weak unless (A) there are a lot of undead in the campaign or (B) you can use your turn attempts on something else.
If you have a positive CHA modifier, you can ask your DM to let you use the SRD feat "Divine Might." (
http://www.d20srd.org/srd/divine/divineAbilitiesFeats.htm#divineMight) It is great and highly thematic.
CLASSES:
You don't want to lose any caster levels. With PHB + DMG that means sticking to cleric. The only possible multiclassing I'd suggest would be from the SRD, the Prestige Paladin (a 1 or 3 level dip) and the Human Paragon (trade Turn Undead progression and one level of spell progression for better skills and a bonus feat, and maybe a Martial Weapon Proficiency in something good like the Great Sword).
FIGHTING STYLE:
Unfortunately, in core only, Sword & Board is a bit underwhelming. If you are stuck with the Long Sword or the Heavy Mace, though, it is probably your best option early on. Later, once you have a decent to-hit and better defenses from spells/HP, you can drop the shield and go two handed on your weapon for superior power attack damage. If you don't like that idea, Magic Vestment can power up your shield some at higher levels.
DOMAINS:
The war domain is a trap, IMHO. The longsword is hardly better than a mace. IMHO, the best core domains are Luck and Travel. Luck has a great Granted Power as does Travel; Travel also has a great spell list. The Strength Domain is also decent due to the Enlarge Person buff.
FEATS:
1 - Divine Might*
1 - Weapon Focus (Weapon of Choice) - Its boring, but +1 to hit is something you'll use in every encounter. You may have gotten this for free with the War Domain, so see below.
3 - Power Attack - Highly handy for a melee type, not useful until you actually have some BAB to burn though! Better if you use a THF style
6 - CHOICE
9 - Quicken Spell
Skill Focus Concentration can also be swapped in for either Divine Might or Weapon Focus. Improved Initiative is another solid choice. Going first lets you drop an extra buff spell before the melee starts.
For the 6th level feat, there are a few choices. If you didn't take WF, SF, or Divine Might earlier, you can sneak it in now. Cleave is usually sub-optimal but it can get you an additional attack occasionally, and might be handy if crowd control is an issue. Improved Bullrush or Sunder can give you more tactical options. Craft Wondrous Item is likely the best crafting feat out there for sheer versatility's sake. Leadership is great if allowed. Mounted Combat is required for Prestige Paladin.