Sounding guardedly optimistic about reaching agreement, OPEC oil ministers gathered here tonight for another urgent try at unifying prices.

But pricing unification, a goal that has eluded the 13-member Organization of Petroleum Exporting Countries for two years, is still not assured. Differences reportedly remain over how high premiums should be for better quality OPEC oil, and there was one hint today of interest in linking new production quotas to a pricing decision.

In addition, the impact, if any, of President Reagan's victory on the AWACS vote will have on the Saudi strategy here remained unclear.

The Saudis have been the leading advocate up to now for reunification of a target price of $34 per barrel of Arabian light crude. This would mean a $2 increase in the base the Saudis now use, in return for a drop in the existing $36 market price used by most other OPEC states.

It could also mean reduction in the premiums allowed for producers of higher quality crude, particularly Libya and Algeria, which now list their oil officially at around $40 a barrel.

But the overall short-term effect of unification would appear to be a slight increase in the weighted average price of OPEC oil. Moreover, to avoid a substantial increase in its own oil prices following Reagan's all-out effort to secure the sale of the planes, Saudi Arabia could hesitate on a pricing move tomorrow.

On the other hand, Saudi Arabian oil minister Sheik Ahmed Zaki Yamani publicly denied any direct link between AWACS and oil in the days leading up to the Senate vote, and OPEC ministers here today referred to Yamani's statement when asked about the effect of the vote.

There are also strong arguments for the Saudis to continue to press for unification now. The move is intended to stop the rapid erosion in OPEC oil sales -- down now to about 20 million barrels per day, or 25 percent below the level this time last year -- by ensuring more stable, predictable prices.

With unification, the Saudis have been insisting that OPEC prices be frozen through the end of next year. This is expected to remain a Saudi condition for any final agreement, and would obviously benefit consumers in the long run.

Because member states are already involved in contract negotiations for 1982 oil supplies, the pricing issue carries a particular urgency for OPEC. Members called the emergency meeting for Thursday rather than wait six weeks for a regular session previously scheduled.