C172 INSTRUCTOR RETURNING TO LAND IS ALERTED BY BWI CTLR OF TFC CONFLICT.

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WE WERE OPERATING OUT OF BAY BRIDGE ARPT (W29) THAT IS CURRENTLY WITHIN THE ENHANCED CLASS B AIRSPACE. BEFORE ENG START; I CALLED BWI APCH VIA TELEPHONE TO GET OUR CLRNC AND SQUAWK CODE. AFTER DEP; I CONTACTED BWI APCH AND FLEW E TO EXIT THE AIRSPACE. RADIO RECEPTION WAS SCRATCHY; BUT READABLE. ONCE CLR OF THE AIRSPACE; I REQUESTED AND RECEIVED A FREQ CHANGE. THERE WERE 3 SOULS ON BOARD; A STUDENT PLT OCCUPYING THE L FRONT SEAT; MYSELF (CFI) IN THE R FRONT SEAT; AND A PVT PLT/INST STUDENT IN THE REAR SEAT. I HAD THE STUDENT PLT PERFORM MANEUVERS AND THEN WE DID FULL STOP LNDGS ON RWY 33 AT EASTON ARPT (ESN). AFTER THE LNDGS; WE DEPARTED ESN TO THE S AND CLBED TO 2000 FT TO OVERFLY THE ARPT (ARPT ELEVATION IS 74 FT MSL). I CONTACTED BWI APCH TO REQUEST CLRNC INTO THE ENHANCED CLASS B AIRSPACE AND TRANSITION BACK TO BAY BRIDGE ARPT. BWI APCH ACKNOWLEDGED RADAR CONTACT AND WE PROCEEDED TOWARD W29. WE WERE STILL OUTSIDE THE ENHANCED CLASS B AIRSPACE WHEN APCH CALLED TFC AT OUR 2 O'CLOCK POS. I RESPONDED THAT WE HAD THE TFC IN SIGHT. THE ONLY VISUAL CLUE OF TFC WAS HIS LNDG LIGHTS (TYPE OF ACFT WAS UNKNOWN TO US). I TURNED ON OUR LNDG LIGHT; WHICH WAS ON THE L WING; OPPOSITE THE INCOMING TFC. I HEARD THE CTLR TALK TO THE INCOMING TFC; BUT DID NOT HEAR ANY RESPONSE TO THE CALLS. I THOUGHT I HEARD THE CTLR SAY; 'IF YOU HEAR ME' TO THE TFC. THIS MADE ME WONDER IF THE INCOMING TFC HAD BEEN WITH BWI; BUT CHANGED FREQ AS HE APCHED ESN. THE TFC SEEMED TO TURN TOWARD US AND APCHED AT A HIGH RATE. THE CTLR SAID; 'SOMEBODY BETTER CLB.' MY FIRST THOUGHT WAS; WHAT HAPPENS IF WE BOTH CLB? I XMITTED THAT WE WERE CLBING AND INITIATED A STEEP CLB. THE BIZJET PASSED ABOUT 500 FT BELOW US; WITHOUT ANY COURSE DEV. USUALLY I WILL TURN TO THE TAIL OF XING TFC; BUT THE CONVERGENCE RATE WAS TOO HIGH. AFTER THE JET PASSED BELOW US THE CTLR THANKED US AND TOLD US TO DSND TO 2000 FT AND PROCEED TO W29. ONE CONTRIBUTING FACTOR WAS THE CTLR SAYING; 'SOMEBODY BETTER CLB.' I KNOW THAT ONCE WE CONFIRM THAT WE HAVE THE TFC IN SIGHT; IT IS OUR RESPONSIBILITY TO SEE-AND-AVOID. THERE WAS VERY LITTLE TIME FOR US TO RESPOND. IF THE CTLR TOLD US (BY N-NUMBER) TO CLB; THERE WOULD HAVE BEEN NO HESITATION OR SECOND THOUGHTS ABOUT WHAT HAPPENS IF BOTH OF US CLB. ANOTHER FACTOR WAS THE SCRATCHY RECEPTION. IT MAY HAVE BEEN DUE TO THE PORTABLE INTERCOM SYS. I FLEW WITH THE PVT PLT/INST STUDENT LATER THAT EVENING. WE DIDN'T USE THE PORTABLE INTERCOM AND THE RADIO RECEPTION WAS MUCH CLRER.