Blue Hills Meteorologist Wallace E. Howell once again yesterday disclaimed credit for the extent of a heavy rainfall in the New York City watershed area.

Under Howell's direction New York City's two silver iodide generators flooded the Catskill skies early Thursday morning. "They may have eked out a few extra hundredths of an inch--let's hope so," said N.Y.C. Weather Bureau chief Ernest J. Christie.

Howell, who is receiving $100 for each day on the job as the city's consultant meteorologist and "rainmaker," repeated his earlier statements that he would make no claims until he has accumulated data on all his attempts through June.

With the Scoharie Reservoir overflowing yesterday, Howell shifted his attack to the Westchester region. The Croton reservoir received only .14 inches of rainfall on Thursday, while Scoharie absorbed .8. Reservoirs now hold 78.5 percent of capacity, as compared to 97 percent at this time last year.

Couldn't Make It

Howell went up in a police plane at 9:30 a.m. Thursday with 150 pounds of dry ice. The plane was unable to got on top of the clouds for seeding and landed again at Floyd Bennett Airport in Brooklyn two hours later.

Weatherman Christie deprecated the role of Howell's silver iodide spray in the downpour by pointing out that light rain had started in the test area before the experiment began, and that the heaviest rainfall had been to the south--not to the north, where the chemical clouds had drifted.