Sonia O'Sullivan yesterday provided something of a surprise by announcing that she would run in the 5000 metres during the opening session of the national track and field championships in the Morton Stadium, Santry today.

O'Sullivan is also entered for the 800 and 1500 metres championships and the expectation is that she would run in one of these.

Her decision to go in the 5000 metres, scheduled to start at 2.25 p.m., was influenced in part by a desire to help Valerie Vaughan and Marie McMahon achieve qualifying standards for the European championships at Budapest next month.

With O'Sullivan to dictate the pace, Vaughan and McMahon believe they are capable of qualifying. Selectors are scheduled to name their squad tomorrow evening. Vaughan, in particular, has good reason to covet European selection, for she was left out of the Olympic squad for Atlanta two years ago after declining to take part in a trial for the third and final 5000 metres nomination.

Today's 5000 metres will be O'Sullivan's last at the distance before challenging for the European 5000 metres title and she plans to use it to test her form three weeks before her biggest challenge of the season.

"At one point, I was considering the 1500 metres but having already run three 1500s and a mile race this summer, I believe I can now get more benefit from the longer distance," she said.

"I'm scheduled to run a 3000 metres race at Gateshead in eight days' time, so I think I've covered all the angles for Budapest. I'm happy with the way I'm running but, at this point, I don't think I will be chasing any records at Santry."

Even without O'Sullivan, this would have been one of the better championship meetings of recent years. Attracted by the prospect of European selection, many foreign-based athletes are returning to compete, ensuring a sharp competitive edge to the programme.

Susan Smith is already assured of challenging for the 400 metres hurdles in Budapest but can still do with a big performance here as encouragement before the tougher tests ahead.

As yet, she hasn't rediscovered the flair which enabled her to make such impressive progress in the international rankings in the past two years, but this may be the occasion when it all begins to come together again.

Emily Maher, properly acclaimed for a superb sprint double during the Olympic youth championships in Moscow, will concede strength and experience to Marissa Smith of Clonliffe in the 100 metres.

Una English, who has returned from Switzerland to live in Cork, is entered for the 800 and 1500 metres and is expected to run well.

While most of those who were expected to achieve qualifying marks for Budapest have already done so, there are still some notable exceptions. In this context, Niall Bruton and Shane Healy will bring some urgency to the men's 1500 metres.

Bruton, brilliant in the mood but prone to inconsistency, is still some way removed from the form which made him an automatic choice in other years and Healy, too, must find significant improvement if he is to make it to Hungary.

By contrast, the young Larne athlete James McIlroy has attained a remarkable rate of development this summer. Coached by Sean Kyle, McIlroy scarcely figured in calculations at the start of the summer but he now rates as one of the brightest prospects on the Irish scene.

All his better runs have been at 800 metres but there is some speculation that he will now switch to the 1500. If he does, it may well provide an additional incentive for the two Dubliners to move up a gear.

Should McIlroy stay in more familiar surroundings, it will bring him on course for a meeting with David Matthews and James Nolan who, no less than Bruton and Healy, will be hoping that the importance of the occasion induces a return to form.

The two Ryans, Neil and Gary, look certain to dominate the men's sprints and, in the field events, there is the promise of big performances by Nick Sweeney, Terry McHugh and Roman Linscheid.

Britain's extensive injury list lengthened last night when Ian Mackie pulled out of the opening round of the 100 metres at the AAA championships in Birmingham because of a knee injury.

Britain's European Championship hopes have been bedevilled by injuries this summer.