Cal Ripken Jr.'s 1999 baseball season, which began with grief and pain and careened from frustration to rejuvenation and back again, ended today when the Baltimore Orioles announced that the sport's one-time "Iron Man" will have surgery Thursday morning to repair his injured back.

Ripken, 39, is expected to be ready for spring training in February, when he would launch his 20th major league season and resume his pursuit of 3,000 career hits. Ripken finishes his season nine shy of that mark and with some of the best offensive numbers of his career.

"He was in a lot of discomfort," Orioles General Manager Frank Wren said after speaking with Ripken by phone tonight. "And he felt it was the time to do it."

The surgery, described as a "decompression" to relieve Ripken's nerve root inflammation, will be performed by specialist Henry Bohlman at University Hospitals of Cleveland. Ripken suffers from a narrowing of the spinal column, which produces nerve irritation. The surgery is expected to eliminate the condition permanently.

Ripken played in a record 2,632 straight games before voluntarily ending the streak last September. This season, however, he twice was placed on the disabled list because of back pain, the first two trips to the disabled list since his career began in 1981.

Ripken's first stint on the disabled list began April 20, less than a month after his father -- longtime Orioles coach and manager Cal Ripken Sr. -- passed away. Ripken also was struggling at the plate, batting .179, and on the field at that time. A recurrence of the injury in August forced him back on the disabled list.

Ripken will be hospitalized for up to three days, Wren said, and could be "up and around" within a month. By the opening of the Orioles' spring training camp in mid-February, Ripken should be 100 percent healthy.

"My understanding is, the surgery will correct that and give more space for that nerve, which will keep it from flaring up," Wren said. "This was inevitable. If he wanted to continue to play at a high level, this needed to be done."

Ripken left the team in Texas this morning to travel to Cleveland, after a fitful night of sleep caused by back spasms.

"He was going to play," said Orioles infielder Jeff Reboulet, "until it stopped him from playing."

The back problems tainted an otherwise rejuvenating season for Ripken. His .340 batting average and .584 slugging percentage are the best of his career and lead the Orioles this season.

He hit his 400th career home run on Sept. 2, and seemed poised to collect his 3,000th hit during the six-game homestand that concludes the season next week. Ripken had been particularly hot in the last 10 games, hitting .484 and picking up steam as he closed in on the 3,000-hit mark.

In July, the Orioles announced they picked up the $6.3 million option on Ripken's contract for 2000.

Ripken's 3,000th hit would have given baseball an unprecedented three new members of the 3,000-hit club in the same season. San Diego's Tony Gwynn and Tampa Bay's Wade Boggs each reached the milestone earlier this season.

Although Orioles head trainer Richie Bancells said there was no single incident that triggered this recurrence, Manager Ray Miller and several teammates noticed Ripken hit the first base bag awkwardly and winced as he slid into second base with a double Tuesday night.

"I held my breath when he hit the double because as he hit the bag and went to take the first step to second, his foot kicked out from under him," Miller said. "Then he had to slide, and it didn't look too pretty. . . . He was real quiet. I asked him if he was okay. He said yes, but then [later] he said, `You'd better get me.' "

Miller removed Ripken from the game in the bottom of the eighth inning, a common occurrence in recent weeks. Ripken appeared fine in Miller's estimation as he lounged in the clubhouse after the game, but Ripken contacted Bancells early this morning complaining of back spasms that prevented him from sleeping, then left for Cleveland late this morning.

Three days earlier in Anaheim, Calif., Miller also noticed Ripken in some discomfort when he was slow getting out of the batter's box on a double-play grounder. Miller thinks it was more than coincidence that Ripken's last two bouts with his back injury came within days of a cross-country road trip.

"I've been worried about this trip all year," Miller said.

Wren said he and Ripken avoided the topic of surgery for much of this season. "He always considered it a last resort. We hoped the other treatments worked, and for a while they did."