David Coulthard is poised to turn down a dream move to partner double world champion Michael Schumacher at Ferrari next season in order to keep his own world title ambitions on course at McLaren.

The Scot, in Hockenheim for tomorrow's German Grand Prix, has been approached by the legendary Italian team to replace their current No.2, Irishman Eddie Irvine.

Ferrari president Luca di Montezemola admitted: ''We have until the end of the month to decide on who will partner Michael (Schumacher) next year.'' But while Coulthard, with one win under his belt already this season and robbed by fate of possibly two others, is currently the front-runner in the McLaren team, a move to Ferrari would see him firmly installed as No.2 to Schumacher.

Such a position would not rest easily with someone as ambitious as the 26-year-old Scot, who has made it clear his preference is to stay with the Mercedes-powered McLaren team, which he believes will become a serious force next year.

''I know I can win the world championship providing I have the right equipment and the opportunity to get the job done,'' Coulthard said yesterday. ''I believe that chance will come at McLaren and that's why I want to stay here.''

The Borders-born Scot is now clear favourite to be retained by McLaren, whose other driver, Finland's Mika Hakkinen, is also out of contract at the end of this season.

Coulthard's manager, Tim Wright, admitted yesterday: ''Talks have started with McLaren. It was always the understanding when we signed with the team for 1996 and 1997 that David's link with McLaren would roll on into 1998 and beyond if both parties were satisfied. That clearly appears to be the case.''

Meanwhile, Coulthard will turn his attention to winning the German Grand Prix in front of 100,000 noisy fans, who will give their support to Michael and brother Ralf Schumacher.

''Hockenheim suits our engine and the car,'' said the Scot, whose car was quickest on the straight last year. ''Both Mika and I are optimistic we can qualify in the top six at least and grab podium finishes.''

Heinz-Harald Frentzen was given a vote of confidence yesterday, blocking a dream return for Damon Hill to Williams.

Technical director Patrick Head said that Williams were unlikely to change their driver line-up in 1998, although he admitted that the team had underperformed this year.

Frentzen's future had been under threat by a series of disappointing displays, with speculation mounting that Hill could return. But Head said: ''I am more than happy with the drivers we have got at the moment. I don't feel we need to consider making any changes, particularly as they are both under contract.

The news means that Hill, who was sensationally dropped last year despite his eight wins, is highly unlikely to make an equally dramatic switch back from Arrows. Hill seems certain to leave Arrows after a disappointing defence of his world title, which has yielded just one point so far.

The opening skirmish was badly affected by rain, which left large parts of the Hockenheimring track slippery. The Schumacher brothers delighted the estimated 80,000 crowd by dominating the session. Jordan-driver Ralf took top spot from Michael by just over a tenth-of-a-second but saw his second practice session curtailed when he spun his car into a tyre barrier.

Johnny Herbert was a fine third for Sauber, but would be content with a top six place in qualifying tomorrow. Hill was ninth, Irvine tenth and Coulthard seventeenth.

Championship favourite Villeneuve was sixteenth, two places ahead of Frentzen. Times from unofficial practice:

1 R Schumacher (Ger) Jordan-Peugeot 1:46.196; 2 M Schumacher (Ger) Ferrari 1:46.322; 3 J Herbert (Gbr) Sauber 1:46.517; 4 R Barrichello (Bra) Stewart-Ford 1:46.526; 5 N Fontana (Arg) Sauber 1:46.706; 6 P Paolo Diniz (Bra) Arrows-Yamaha 1:46.873; 7 S Nakano (Jpn) Prost-Mugen-Honda 1:47.143; 8 M Hakkinen (Fin) McLaren-Mercedes 1:47.386; 9 D Hill (Gbr) Arrows-Yamaha 1:47.542; 10 E Irvine (Gbr) Ferrari 1:47.594; 11 J Verstappen (Ned) Tyrrell-Ford 1:47.720; 12 J Magnussen (Den) Stewart-Ford 1:47.769; 13 J Trulli (Ita) Prost-Mugen-Honda 1:47.784; 14 G Berger (Aut) Benetton-Renault 1:47.887; 15 J Alesi (Fra) Benetton-Renault 1:48.455; 16 J Villeneuve (Can) Williams-Renault 1:48.639; 17 D Coulthard (Gbr) McLaren-Mercedes 1:48.648; 18 H-Harald Frentzen (Ger) Williams-Renault 1:48.958; 19 G Fisichella (Ita) Jordan-Peugeot 1:49.010; 20 T Marques (Bra) Minardi-Hart 1:49.563; 21 M Salo (Fin) Tyrrell-Ford

1:49.831; 22 U Katayama (Jpn) Minardi-Hart 1:51.058.

q Scot Dario Franchitti lines up for tomorrow's US 500 Indycar race knowing he has achieved one of the targets he set himself for his rookie season. Now he has every intention of succeeding in the two others.

''At the start of the year I said to myself I wanted to take one pole position, to win a race, and win the rookie-of-the-year title,'' the Carl Hogan Racing Team driver said in Michigan yesterday. ''I took pole last week in Canada - now we'll have to see what happens with the others.''