If one has made a rollover from an regular IRA to a Roth IRA prior to 1999 and is eligible for the four year averaging option, can one elect out of this option and increase his tax payment in a given year, resuming the averaging in subsequent years.?

Nope!

Not that I am advocating taking distributions from your IRA (which may not even be an issue for this topic, since the four year period for 1998 conversions ended in tax year 2001)… any distribution from the Roth IRA during the four-year period would result in an acceleration of the taxable income from the conversion.



For example, if you converted $100,000 the income would be spread over four years as follows:
1998-$25,000
1999-$25,000
2000-$25,000
2002-$25,000

Assume that you distribute $20,000 from the Roth IRA in 1999… the taxable amount in 1999 would be $45,000 ($25,000 + $20,000). The taxable amount for the last year would be reduced by amounts withdrawn during the four-year period.

In summary, the only way to “increase his tax payment” is to take a distribution during the four-year period.