Seattle Slew is the glamour boy of thoroughbred racing at the moment, but it is the old pro. Forego, which commands national attention today in the $115,900 Metropolitan Mile at Belmont Park.

Forego has been the national champion the last three seasons, clearly the best race horse to appear since Secretariat. Now, 7 years old, the 17-hand gelding would seem to have the most interesting year ever ahead of him in 1977.

His objectives are a successful try, on the fourth attempt, at the Handicap Triple Crown, to surpass Kelso's record earnings figure of $1,977,896 (ForeFogo ranks third with $1,670,217) to continue his reign as horse of of ofthe year, moving within one of Kelso's 1960-1964 string, and in so doing defeat Seattle Slew.

Of the four objectives, the easiest should be Kelso's dollar mark. Given any luck at all, Forego will be over the $2 million level by the fall, when the weight-for-age classics give him a fair shake against younger rivals.

The Handicap Triple Crown again will be difficult. Forego must carry higih weight of 133 pounds in the Met, the opening event, conceding six to 30 pounds to 14 foes, several of which appear extremely dangerous at the weights. Soy Numero Uno, under 127 pounds. It's Freezing, 116, and the entry of Barrera, 117, and Due Diligence, 112, all promise to make the mile extremely competitive as Forego seeks his 31st victory in 50 career starts.

Forego's failure to win all three of the handicap races in one season has not been for lack of trying. Last year he missed by a nose - to Foolish Pleasure in the Suburban - while winning the Metropolitan and Brooklyn, the latter for the third straight time.

Only three horses have swept the three races. They were Kelso in 1961, Toom Fool in 1953 and Whisk Broom II in 1913. That is elite company, and none of those three ever had to carry the weight Forego must shoulder this year. Kelso, for example, began his successful quest under 130 pounds in the Met.

Seattle Slew was assigned 119 pounds for today's feature. That is six over sccale for a 3-year-old, the same as Forego is six over scale for an older horse. Racing secretary Tommy Trotter obviously believes these two runners will make for an epic race when they meet. So does everyone else.

Slew was never seriously intended for the Metropolitan. Trainer Billy Turner is not about to risk his colt's undefeated status against Forego, not with the Belmont Stakes just around the corner on June 11 and no 3-year-old ever having completed that Triple Crown unbeaten.

It will be September before Forego and Seattle Slew get together.

The strike by mutuel employees continues in New York. ItI began May 20, when Aqueduct was shut down. The New York Racing Association offered racing for Off-Track Betting only last Mondaay through Thursday, then had wagering Friday and Saturday without the union clerks. Six other unions supported the strikers innn protest Saturday, but 17,000 fans turned out and bet nearly $2 million.

A rival or two for Seattle Slew in the Belmont probably will emerge from today's $124,200 Jersey Derby at Atlantic City. For The Moment and Cormorant, the speed horses that tried the favorite in the Kentucky Derby and Preakness, are entered in the Jersey's field of seven but it is Iron Constitution favored in most overnight lines. I'll go with Cormorant.

Iron Constitutions is making his sixth start in six weeks, with the Belmont certain to be the seventh in eight weeks. One wonders if the owner will be able to find a prep race for his gray colt between the Jersey Derby and the Belmont.

It takes an animal with an iron constitution to hold up under such a schedule, but Iron Constitution has won the Withers Mile and was second in the Preakness the last two weekends, finishing ahead of Cormorant on both occasions.

Pimlico's strike-delayed meeting ends today with What A Summer set to spot six fillies and mares from nine to 19 pounds in the Nellie Morse Handicap. She is odds-on favorite.

Bowie opens Tuesday.