WE PROPOSE TO USE FERMI LAT DATA TO STUDY THE INTERSTELLAR GAS AND COSMIC RAYS (CRS) IN THE INNER MILKY WAY. THE RESULTS WILL ADDRESS SOME OUTSTANDING ISSUES CONCERNING THE DISTRIBUTION OF CRS AND INTERSTELLAR GAS IN THE DISK OF OUR GALAXY: 1) IS THERE OBSERVATIONAL EVIDENCE FOR AN ENHANCEMENT OF CR DENSITIES IN THE INNER GALAXY AS EXPECTED IF THE ACCELERATORS ARE SUPERNOVA REMNANTS AND MASSIVE-STAR FORMING REGIONS? 2) HOW DO CRS PROPAGATE AWAY FROM THEIR SOURCES ON SMALLER SCALES IN THE TURBULENT REGIONSAROUND THE ACCELERATORS AND ON LARGER SCALES THROUGHOUT THE MILKY WAY? 3) ARE THERE ANY LARGE-SCALE VARIATIONS OF THE CO-TO-H2 RATIO POSSIBLY RELATED TO METALLICITY EVOLUTION ACROSS THE GALAXY? ALTHOUGH MODELING GAMMA-RAY EMISSION WITHIN THE SOLAR CIRCLE IS CHALLENGING BECAUSE OF THE PILE UP OF MULTIPLE STRUCTURES ALONG THE LINE OF SIGHT WE HAVE IDENTIFIED AS SUITABLE TARGETS THE DIRECTIONSTANGENT TO SOME OF THE SPIRAL ARMS NAMELY THE SAGITTARIUS SCUTUM CENTAURUS AND CARINA ARMS FOR WHICH A LARGE FRACTION OF THE GAS IS CONCENTRATED IN THE TANGENT POINT WITH A WELL-DEFINED LOCATION IN THE GALAXY. WE WILL BE ABLE TO DETERMINE FOR THE FIRST TIME THE GAMMA-RAY EMISSION RATE PER H ATOM IN REGIONS WITH WELL-DEFINED LOCATIONS IN THE INNER GALAXY DERIVED FROM THE GAMMA-RAY EMISSIONMORPHOLOGICALLY ASSOCIATED WITH THE COLUMN DENSITIES OF ATOMIC HYDROGEN FROM RADIO OBSERVATIONS. WE WILL THEREFROM CONSTRAIN THE CR DENSITIES USEFUL TO STUDY THE CORRELATION WITH PUTATIVE CR SOURCES LIKE SUPERNOVA REMNANTS AND MASSIVE-STAR FORMING REGIONS AND TO TEST DIFFERENT CR PROPAGATION SCENARIOS. WE WILL ALSO DIRECTLY COMPARE THE AVERAGE CR DENSITY WITH THE STAR-FORMATION RATE FOREACH REGION AND PROBE FOR LOCALIZED CR ENHANCEMENTS POSSIBLY RELATED TO INDIVIDUAL CR SOURCES. AT THE SAME TIME CRS WILL BE USED AS PROBES TO DETERMINE THE MASSES OF THE INTERSTELLAR COMPLEXES IN THE TANGENT POINTS NOTABLY TO CALIBRATE THE CO-TO-H2 RATIO IF ATOMIC GAS AND MOLECULAR GAS TRACED BY CO EMISSION IS ILLUMINATED BY THE SAME CR FLUXES. THEREFROM WE WILL OBTAIN IMPROVED CONSTRAINTSON POSSIBLE VARIATIONS OF THE CO-TO-H2 RATIO IN THE MILKY WAY. THE WORK PRIMARILY WILL CONSIST IN MODEL BUILDING FOR THE LIKELIHOOD ANALYSES FOR EACH OF THE REGIONS TO BE STUDIED. WE WILL CONSTRUCT MULTIWAVELENGTH MAPS OF THE INTERSTELLAR MEDIUM TRACERS THAT WILL BEUSED TO MODEL THE DIFFUSE GAMMA-RAY EMISSION INCLUDING ATOMIC GAS MOLECULAR GAS TRACED BY CO AND DARK NEUTRAL GAS TRACED BY DUST. THE KINEMATIC SEPARATION OF ATOMIC HYDROGEN STRUCTURES ALONG THE LINE OF SIGHTS POSES A SERIOUS CHALLENGE DUE TO THE LARGE WIDTH OF THELINES (5-10 KM/S) AND TO SELF-ABSORPTION FEATURES THAT WE WILL ADDRESS WITH THE DEVELOPMENT OF A REFINED SEPARATION TECHNIQUE BASED ON FITTING THE LINE PROFILES.WE WILL ALSO TAKE INTO ACCOUNT THE DISTRIBUTION OF DARK NEUTRAL GAS ALONG THE LINE OF SIGHT BY USING EXTINCTION DATA AND REALISTIC MODELS OF STELLAR POPULATIONS IN THE MILKY WAY TO DERIVE THE DUST EXTINCTION PROFILE WITH DISTANCE. IN ADDITION WE WILL REFINE THE MODELS FOR THELARGE NUMBER OF GAMMA-RAY POINT SOURCES IN THE FIELDS STARTING FROM THE LAT SOURCE CATALOGS AND REFINING THEM ITERATIVELY IN THE FIT TO THE DATA AND WE WILL USE VARIATIONS OF REALISTIC MODELS OF LARGE-SCALE INVERSE-COMPTON EMISSION FROM THE GALAXY TO GAUGE THE RELATEDSYSTEMATIC UNCERTAINTIES.