ऋचो अक्षरे परमे व्योमन यस्मिन देवा अधि विश्वे निषेदुः |
यस्तन्न वेद किमृचा करिष्यति य इत्तद्विदुस्त इमे समासते || RV .1.164.39 ||
This Rishi of this Mantra is Dirghatamas and is Known as "Asya Vamiya Sukta " . The Mantras 1-41 are dedicated to Vishwadeva.
In this Mantra Dirghatamas is pointing towards those who do not know the Imperishable Brahman.Rishi Dirghatamas Is also saying that what use the Vedas would be to a person who does not know the characteristics of Brahman because Vedas are a in the Brahman, who is like space and never changing. All the gods rest in Brahman. If a person knows nothing about Brahman but only performs rituals and rites what will he gain? On the opposite those who know Brahman, as it were, live like as they are one with Brahman and attain Bliss .
This Sukta is Of type VedaGyana -Prashansa i.e. in praise of Knowledge in the Vedas .The manta 39 of which speaks of the syllable ( akshara ) that exists in the divine. Here in this mantra the word Richas ऋचा is to be taken as all the Vedas.
Let's first of all see what the western as well as Indian translators has translated the mantra.
H.H.Wilson with Commentary of Sayana
All the gods have taken their seats up this supreme heaven , the
imperishable (text) of the veda : What will he , who knows not this ,
do with the veda ? but they who know it , they are perfect.
Pandit Shriram Sharma Acharya
Indestructible Richa's (vedas) are contained in supreme Vyoma (i.e.
Vast Akasha ) , all godly powers resides in that. What Richa's (vedas)
do for him who do not know this truth , those who know this truth do
make a good use of this Richa's (vedas) .
Rigved Subodh Bhashya by Satavalekar Damodar
The Paramatma is like the Vast space and indestructible like
aksharas of vedas. All the gods resides in that Paramatma. Who does
not know this Parabrahman ,what they will do with these Veda mantras.
Those learned who knows this Param-Tatva , dwells in the higher
This same Rig -Veda manta is also found in Atharva Veda 9.10.18
and in The Shvetashvatara Upanishad 4.8
We are having a good commentary of Shree Adi Shankaracharya on same mantra in the Shvetashvatara Upanishad . Lets see what he is saying.
ऋचो अक्षरे परमे व्योमन् यस्मिन्देवा अधि विश्वे निषेदु : |
यस्तं न वेद किमृचा कारिष्यति य इत्तद्विदुस्त इमे समासते ||4.8 ||
8 The vedas are established on the imperishable supreme space where
all the gods dwell . What will one achieve through the Vedas , who
does not know it . thus they who are such , remain self-fulfilled.
Shankara's Commentary - :
Rcah the Vedas ; are established aksare , in the imperishable ; Parame
, supreme : Vyoman (i.e. vyomni) , space - comparable to space - ,
which is known from the three vedas ; and yasmin , where ; visve
devah , all the gods ; adhiniseduh , dwell , stay supported . Kim
karishyati , what will one achieve ; rca through the vedas ; yah , who
; na veda , does not know ; tam , it? ye , those who ; viduh , khow ;
tat ; it , thus ; te they ; are such ; samste , remain self fulfilled.
Now as of your enquiry is this अक्षरे - imperishable syllable indicates Om?
From looking at all the translations above ,it is clear that none of them supportive to the notion that this Aksara here is denoting sacred letter "OM". Adi Shankara in his commentary is saying that the Aksharas of vedas are residing in that Parabrahman , who is supreme and vast like the space.
Shree Satavalekar is also explaining that this Akshras of Richas (vedas) are like that of Paramatma who is also indestructible.
And also according to Very well known vedic scholar Shree Siddheshwar Shastri Chitrav , the notion of Akshara is presented as Atma or Parmatma only in his commentary of this mantra which is in Marathi. i am enclosing a screenshot of it below.
The Only exception is Yaskacharya Sanskrit grammarian (4th c. BCE ) whose views are mentioned in this Shodhganga
Article (PDF ) -Page 35.
That this Aksara" is "Om" . Of the phrase " rco akshare parame
vyoman," found in the above hymn,' Yaska in his Niruktd has an
enlightening explanation.According to him "Aksara" is "Om" on which
all the gods repose. 'Those who do not know this Supreme Word; what
can they do with 'rcah' only, and those who know it are, well placed'-
is the advice of the learned.
What is that word - “aksara” ? Yaska says “ It is "Om", in the
opinion of Sakapuni”.43 (Sakapuni” was an ancient Grammarian).44
Therefore, here, 'Om' is the Ultimate Reality ('Brahman') on which
everything, (including Vak) rests
So here we see the two sides one side is all the available translators and on the other Sanskrit grammarians "Yaska" who is saying this on the opinion of Sakapuni a another ancient Grammarian that Aksara" . is "Om"
In this case coming to any conclusion is tricky part.
But in conclusion - Considering central meaning of all the current translations and seeing that none of them is supportive to this notion that word Aksara is denoting "OM" , and mainly taking the help of Adi Shankara's expanaton. The word Aksara here , which are akshara's of Vedas are equated with ParamAtma in this manta , and is pointing towards supreme Brahman . So we can safely say that there is very faint possibility that this अक्षरे - imperishable syllable here indicates Sacred letter "OM".