BALTIMORE, SEPT. 24 -- Laurel Race Course officials today invited Polish champion Omen to next month's Washington, D.C. International, track owner Frank De Francis said.

The invitation is the second of three De Francis can issue under the race's two-tier system initiated last year. The first went to the Soviet Union, which said it will send two of its best horses to Laurel and enter one in the International, a 1 1/4-mile turf race set for Oct. 31. A Soviet horse last ran in the International in 1966.

De Francis said the Soviet horses and a five-person team plan to fly Oct. 5 from Moscow to Frankfurt, where the Poles likely would join them, and continue here Oct. 6.

"The Poles really actively sought the invitation," De Francis said. "The way it's materializing, we expect the International to truly be the Olympics of racing."

Omen, a 3-year-old, has won four races and placed twice in six starts this year. Last year, the Poles sent Korab to the International. The 4-year-old, unraced in nearly three months, finished eighth to U.S. representative Lieutenant's Lark.

Under the two-tier format, nominated horses compete for a $750,000 purse, the three invitees for a $400,000 purse (with all expenses paid).

"When I changed the nominating system {for 1986}, people thought I was nuts," De Francis said. "We were offering a purse of between $400,000 and $600,000, but I was afraid the parade was going to pass us by. I wanted to keep the true international flavor of the race. That's when I came up with the two-tier idea. Now, with that format, we can attract the best horses in the West and add to that by inviting some of the brightest stars from other places, like the Eastern bloc nations."

Among the International's 94 nominations are England's Sir Harry Lewis, winner of the Irish Derby; the United States' Talakeno, who ended champion Manila's winning streak in last month's Bernard Baruch at Saratoga; France's Triptych and Groom Dancer, each a Group I winner, and Tony Binn, one of Italy's top handicap horses.

The International will touch off a weekend "turf festival" at Laurel. The following day, the Laurel Futurity (for 2-year-olds) and Selima Stakes (for 2-year-old fillies) will be run on grass for the first time.