We report the results of a deep spatial , spectral , and timing analysis of ROSAT HRI and PSPC observations of the edge-on starburst galaxy NGC 253 .
In this first paper , point-like X-ray sources detected within the galaxy and in the field are discussed .
The sources are characterized by their X-ray properties ( including comparisons with results from the Einstein and ASCA satellites ) , by correlations with other wavelength and some optical spectroscopic follow up observations .

In total , 73 X-ray sources have been collected in the NGC 253 field , 32 of which are associated with the disk of the galaxy .
Though 27 of these disk sources are detected with the HRI ( some being resolvable with the PSPC ) , the remaining 5 PSPC-only detected sources are likely not to be real point sources , being instead due to fluctuations within the X-ray structure of the disk .
The source close to the center of the galaxy is extended ( L _ { x } \sim 1 \times 10 ^ { 39 } erg s ^ { -1 } in the ROSAT 0.1–2.4 keV band ) , and is most likely associated with the nuclear starburst activity .
The remaining sources have luminosities ranging from 7 \times 10 ^ { 36 } erg s ^ { -1 } to 3.0 \times 10 ^ { 38 } erg s ^ { -1 } , yielding an integrated point source luminosity of 1 \times 10 ^ { 39 } erg s ^ { -1 } .
The brightest point-like source is located \sim 20 ^ { \prime \prime } south of the nucleus , at the border of a plume of diffuse X-ray emission .
Its high X-ray luminosity , time variability and hard spectrum make it a good candidate for a black hole X-ray binary .

Including four Einstein detections of X-ray transients the number of point-like X-ray sources in NGC 253 increases to 30 sources , 13 of which are time variable .
These time variable sources are all brighter than 5 \times 10 ^ { 37 } erg s ^ { -1 } and most likely represent X-ray binaries radiating close to or at the Eddington limit .
Besides the nuclear source there is only one source above this luminosity that shows no time variability and therefore may represent a young supernova or extremely bright supernova remnant , or an unresolved cluster of several X-ray sources .
The point source population of NGC 253 is compared to that of other galaxies , and it is shown that the luminosity distribution matches ROSAT results obtained for M 31 and M 33 .

The halo of NGC 253 is filled with diffuse , filamentary X-ray emission .
Seven sources are located ( or projected ) in this diffuse emission region .
Time variability arguments , together with optical identifications , are put forward to explain 4 sources as background objects , the other 3 sources likely being spurious detections caused by local enhancements in the diffuse emission of the halo of NGC 253 .
The diffuse X-ray emission components of NGC 253 will be discussed in a separate paper .

The sources detected in the field outside the disk of NGC 253 cover a flux range from ( 9 - 300 ) \times 10 ^ { -15 } erg cm ^ { -2 } s ^ { -1 } in the 0.1–2.4 keV band .
None of the sources in the field correlate with published lists of globular cluster candidates .
Optical counterparts are proposed for 27 of them , and a few also correlate with radio sources .
While two sources are identified as foreground stars , the remaining ones are mostly background active galactic nuclei .