UPDATE 2-Oil edges up, but still set for worst H1 performance in 20 yrs

* Oil prices in H1 have fallen the most since 1997

* Analysts doubt OPEC's ability to tighten the market

* Rising U.S. output undermines OPEC-led efforts to cut (Adds comment, updates prices)

SINGAPORE, June 23 (Reuters) - Oil edged up on Friday, recovering some of its steep falls earlier in the week, but crude is still set for its worst first-half decline in two decades despite ongoing production cuts.

Brent crude futures were at $45.33 per barrel at 0647 GMT, up 11 cents, or 0.2 percent, from their last close.

U.S. West Texas Intermediate (WTI) crude futures were up 9 cents, or 0.2 percent, at $42.83 per barrel.

Oil prices have fallen about 20 percent this year despite an effort led by the Organization of the Petroleum Exporting Countries (OPEC) to cut production by 1.8 million barrels per day (bpd) that has been in place since January.

That's the worst first-half performance for crude oil since 1997, when rising output and the Asian financial crisis led to sharp price falls.

Prices are also still down around 15 percent since OPEC extended on May 25 its cuts to cover the first quarter of 2018 instead of expiring at the end of this month.

The weak markets are a result of doubts over OPEC's ability to rein in a fuel supply overhang that has dogged markets since 2014 as production has largely outpaced consumption.

"The post-OPEC meeting slide in prices has lasted longer and pushed lower than we had anticipated in late May," U.S. bank JP Morgan said in its half-year outlook.

"Oil and products comprise five of the ten worst performing commodities this year, owing more to excess supply than to below-average demand," it added.

JP Morgan is not just bearish in its short-term outlook.

"By early 2018, the combination of record U.S. production and deteriorating OPEC compliance probably returns average prices to the mid-to-low $40s," it said.

At the heart of the glut is that the recent efforts to reduce production from the traditional suppliers of OPEC and Russia has been met by soaring output from the United States.

Thanks to shale drillers, U.S. oil production <C-OUT-T-EIA> has risen by over 10 percent in the last year to 9.35 million bpd, close to the level of top exporter Saudi Arabia.

Excess production has left storage tanks bloated.

"Inventories through April are up 80 (million barrels) since the beginning of the year, raising market concerns about the efficacy of OPEC market management," said U.S. bank Jefferies.

"We remain of the view that inventories will draw by 1.5 million bpd in the second half (of 2017), but empirical evidence of this is likely necessary for oil prices to inflect into an upward trend," it added.

(Reporting by Henning Gloystein; Editing by Christian Schmollinger and Joseph Radford)