Good Friday saw the first dismounted patrol by U.S. troops in Baghdad since U.S. armored forces took the city ten days ago - and among the soldiers walking cautiously through the dusty streets of the Mansour District a sharp-eyed observer could make out four men whose headgear -- or lack thereof - and equipment marked them out from the G.I.s.

When the patrol stopped to talk to the amazingly friendly, curious locals, it was one of the men not wearing the distinctive U.S. helmet or body armor who was able to communicate in Arabic and who warned the others not to stare too longingly at the Iraqi women who smiled at them from upstairs windows. The elite, highly secretive British SAS - the special operations group that inspired America's Delta Force -- are in Baghdad.

The Post can reveal that members of the Special Air Service regiment are currently working alongside American troops here - the only British troops to be operating North of Basra - and have been here in secret for some time. They wear American uniforms and travel in American vehicles to minimize their profile.

On their arrival in the Iraqi, the troopers' first mission was to liberate the British embassy, which has been closed since 1990. (They found that it was "in pretty decent condition" having been maintained without pay for 14 years by a faithful employee).

Since then they have been engaged in a variety of missions.

And they have been supplying peacekeeping and policing expertise gained in Northern Ireland, Sierra Leone and elsewhere to a number of American Army units that have begun to shift from combat operations to what the U.S. military calls SASO (Stabilization and Support Operations).

One such unit is the Recon or Scout platoon of the US. Army's 64th Armoured Regiment. The very first American unit in Baghdad to engage in "presence patrols" in humvees and on foot rather than in tanks and APCs, the Scout platoon includes veterans of Bosnian and Kosovar peacekeeping. Some of their senior NCOs have worked with the SAS before.

They are under orders to refer to their SAS colleagues only as "our friends" on the radio or even in conversations with soldiers from other units (though in practice they refer to them as "the Regiment'"

"It's amazing just to watch them operate" Staff Sgt Gannon Edgy said of the SAS men, "the way they blend in in the street, the way they look so relaxed but are so alert to everything around them."

His colleague, platoon sergeant Michael Anslinger noted the SAS troopers' modesty, "they're not like our Special Forces guys, they don't have that arrogant attitude."

For their part the SAS soldiers are impressed by the Scouts' professionalism and willingness to listen to their advice on "hearts and minds" issues:

"These guys are very good, in fact they're the best of the American units we've been working with" said Sgt. D.

The Americans and Brits have also been exchanging rations (each preferring the other country's) and slang. Words like "tosser" and "bugger" delivered in mock English accents are becoming currency among the G.I.s, while the SAS men have begun to use American military argot like "squared away" and to refer to sleeveless vests as "wife-beaters.'

In the early hours of Easter Sunday, some of the SAS troop went out with a Recon section on the first American dismounted night patrol. The Scouts moved silently in ranger file (single file but a grenade blast apart) through the narrow, rubbish strewn alleys of a poor West Bank district. And as the patrolling soldiers kept to the shadows, occasionally dropping to one knee to scan the river banks with night vision goggles, the SAS troopers alternated "on point" with their American comrades.