Ailing Derrick Jackson, Georgetown University's star basketball guard, will not play against Dayton in Tuesday's National Invitation Tournament quarterfinal game, Hoya Coach John Thompson said last night.

Jackson is still hospitalized, recovering from a flareup of a bleeding ulcer. His doctors were not scheduled to make a decision on his availability until tomorrow. But Thompson arbitrarily made his own decision yesterday, adding "at this point we do not expect Derrick to play the rest of the tournament.

"The doctors haven't said he could not play, but they haven't said he could play, either," said Thompson. "It's harder on the other players mentally than it is on Derrick to prepare not knowing his status. It's also precautionary. We can't gamble with Derrick's health. He'd be better of getting totally well at this point."

Jackson accompanied team physician Carl MacCartee to Charlottesville, Va. Wednesday as the Hoyas won 70-68, in overtime. They were the only visiting team to win in eight first-round games and Thompson said he would like to follow the same procedure in the 8:15 p.m. game at Dayton, where the Flyers are 17.2 this season.

Jackson's absence has altered Georgetown's preferred style of basketball. A major characteristic of the Hoyas' most successful season (22-6) is that they have been a team for all tempos.

But Thompson has preferred a fastpaced game because of his team's quickness and Jackson and John Duren's sharpshooting ability. Without Jackson, the area player of the year, Thompson says a more cautious game is beneficial to the Hoyas.

Thompson wants his offense, which son, tooffset Jackson's absence with more inside scoring.

Until Jackson fell ill the afternoon of the Hoyas's ECAC playoff loss to Virginia Commonwealth, Georgetown had used a full-court press after every successful designed more to speed up the pace than to result in steals.

The objective: Get the other team into a shooting contest on the run. And Jackson and John Duren would outshoot them from 15-20 feet over the long haul.

But, without Jackson, Thompson says such a strategy would backfire against a deliberate team.

"We've got to be very careful about our shot selection at this point," Thompson said. "I felt Virginia (Georgetown's 70-68 overtime victim in the NIT's first round) would not get into a running game with us. Virginia would say, 'You take it, but we're going to take our time. We're going to get the foul or we're going to get the basket.'

"They're going to end up getting into the bonus situation and we're going to end up shooting shots that won't get us in the bonus situation. Against a team like that, you've got to be more careful . . . getting it where you want it because you don't want the same shot taken when Derrick Jackson's not in the game.

Whatever tempo Dayton decided on, the Flyers probably will benefit most from the NIT's regional setup. This has given them two straight home games because their arena seats 13,400 and given Georgetown two road games because McDonough gym seats only 4,500.

Friday night's 108-93 first-round victory over Fairfield gives Dayton a 17-2 home-court record this season. The Flyers are 19-9 overall. Among their victims at home are three NCAA Tournament teams: Notre Dame, Syracuse and Miami of Ohio.

All four NIT quarterfinals will be played Tuesday night. The other matchups are Detroit at North Carolina State, Indiana State at Rutgers and Nebraska at Texas. The winners advance to New York for the semifinals Sunday. The semifinal pairings will be made after the teams are determined.

For Georgetown, Jackson's absence also puts new responsibilites on Duren, the sophomore point guard. He has to look more for his own shot and also has to settle the offense.

"Your have to remember that he's only a sophomore, said Thompson. "Nothing makes up for experience." Therefore 5-foot-8 senior Mike Riley, the team's defensive ace, also will be relied on to stabilize the offense.

The Hoyas are looking inside more now to Craig Shelton and Ed Hopkins. Thompson said he will be pleased if Craig Esherick, Jackson's replacement, can score 10 points a game.

"The club has been very fortunate when you think of it," Thompson said. "We still have offensive problems inside, especially if Shelton isn't going well . . . if Hopkins is having a bad day and we can't get it to Craig, we're really having a problem.

"We surprisingly got so much scoring early in the season out of our guards - John came into his own - that it was just a double punch. We had so much going for us, we really didn't need a lot of scoring inside. With Derrick gone, it's got to be made up on the front line."

Tickets priced at $6 and $5, with a $2 discount for students will be on sale at the Georgetown box office tomorrow and Tuesday.