The 109th British Open golf championship begins its four-day run Thursday over the revered Muirfield course, home of the Royal Company of Edinburgh Golfers, and two of the favorites to win this conveted title are reluctant to be considered players to beat.

Severiano Ballesteros, the young Spaniard who added this year's Masters crown to the 1979 British Open title, headed straight for the driving range after today's practice round. He said he had nothing to add to his earlier comments when he complained his game has not been right for several weeks. "It is just the swing that is the problem," said Ballesteros, who has placed in the top 20 only once since winning the Martini tournament in May.

Lee Tervino was talkative as usual, but feared the cool, damp Scottish weather was not suitable for his game. "I don't fancey myself in cold weather," he said. "The two Opens I've won here (including the 1972 tournament at Muirfield) have been in hot weather. I'm not a cold-weather player."

While much of the United States is suffering from a heat wave, and Tervino was a winner in the stifling temperatures of Memphis three weeks ago, the British islands are in the midst of a nonsummer, with temperatures occasionally falling into the 40s.

The sun did shine over the Scottish east coast today, but rain is predicted for Thursday, with winds expected to grow stronger after the completiion of precipitation. Ironically, that could help Trevino, who although he hates to be forced into heavey clothing ("I like to take clothes off"), has a game suitable for ducking the high winds.

Tom Watson, who is only $80,000 shy of the U.S. money record of $462,636 he set last year, is listed as the 6-to-1 favorite by bookmakers here. $4

Jack Nicklaus, a winner at Muirfield in 1962, is listed at 7 to 1; Ballesteros at 10 too 1; Trevino and Ben Crenshaw 14 to 1, and Isao Aoki, the marvelous short-game artist from Japan who hounded Nicklaus all the way as the Ohioan captured the U.S. Open at Ballustrol last month, is at 16 to 1.

Some late, heavey wagering has dropped Greg Norman to 25 to 1. Norman, a 25-year-old Australian, is little known in America, but is the leading player this year on the European tour, having won the French and Scandinavian Opens and having placed in the top eight of 12 events. He is noted as a long, straight hitter who is more fallible near the greens. His countryman, Peter Thomson, golf star-turned-television commentator, said Noran "is nearly right to win) but not quite."

Others among the favorites here are Gary Payer, Hubert Green, a pair of young British stars -- Nick Faldo and Sandy Lyle -- and Des Smyth, the pride of Irish golf since the aging of Christy O'Connor Sr.

This is the 12th Open to be conducted at Muirfield, considered the fairest of the 14 courses used for this event. The stroke record for the event here is 278, by Trevino in 1978. Trevino, Nicklaus (1966) and Walter Hagen (1929) are the only American victors over this links, bounded on the east by the Firth of Forth, near wher it adjoins the North Sea. The famed Harry Vardon (1896) and Henry Cotton (1948) were winners here and the Scottish giant, James Braid, won twice, in 1901 and 1906.

The Royal Company of Edinburgh Golfers can trace its roots to 1744. The present course was designed by old Tom Morris and opened in 1891, making it a young course by British Open Standards.

Although Nicklaus feels putting will make the difference over this course he loves well enough to have named his club in Ohio after it, the Firth of Forth, with its tricky winds, may be a factor. There are no parallel fairways here, so players, when struck by wind, must adjust from hole to hole.

The fairways are narrow -- only a 20-yard landing area greets the field of 151 on the first hole -- and slender yards from the fairway lurks rough strong enough to tear the shoes off a golfer planting a good foothold for a shot.

There are only two blind shots, however -- the second on No. 10 and the tee shot over a hill on No. 11. One also can go blind trying to find a fairway among the bomb craters of bunkers that cross the 17th fairway, suitably placed to discourage the shorter hitter from attempting to reach that 542-yard, par-5 hole in two shots..

Today's paid attendance for the practice rounds was 1i,546, making a record two-day total of 25,522. For the first time, the finishing round will be played on a Sunday -- a victory for American television -- and that promises attendance figures sufficient to generate the record payoff of 25,000 British pounds (about $60,000) to the winner.

Today's play was lighthearted. Playing along with one group was the 73-year-old Cotton, patriarch of British golf, a three-time champion of the Open, beginning in 1934. He was allowed to play from the members' tees, so avoiding some of the 6,926 yards of the par-71 layout, but was observed hitting a wood from the rough on N0. 15 finely onto the green, and following up with an iron smartly to the center of the green at the par-3 16th.

Today, there was banter on the tees and golfers played mainly with tour friends.

Watson and Nicklaus joined together with Andy North and Faldo in a "friendly" foursome.

As they stepped to the 11th tee, it became apparent how somberly they had approached their final practice.

North to Watson: "Are you going to spring for ice cream?"

North: "He doesn't want to break his 10 pounds (Brisith money). It's only 25 (pence). Nick (Faldo) will spring."

Nicklaus: "All he (Watson) does is make birdies and take your money." To Watson: "Are you going to listen to him (North)?"

Watson: "I tried to stop listening to him 10 years ago."

Nicklaus: "Just buy the ice cream and he'll stop talking."

Starting Thursday, there will be little talk of ice cream. And Henry Cotton will be a spectator. The giants of golf will do battle with the bunkers of Muirfield . . . while keeping an ear out for the winds of the Firth of Forth.