Grete Waitz matched the world women's record for the marathon today, finishing in 2 hours 25 minutes 29 seconds and renewing her claim to be the best female long-distance runner in history.

Her time in the third annual London marathon equaled the record set by New Zealander Allison Roe in the 1981 New York City marathon. The win was the first for Waitz in the 26.2-mile distance since her string of victories from 1978-80 boosted women's marathon running to a par with men's for competitive excitement.

But it was a bittersweet victory. Desperate to regain her world-best status, Waitz at first was timed at 2:25:28, one second inside Roe's record time.

She told a news conference later, "I don't usually run for records, but this time I had to. I had some problems during the race with both my knee and my thigh muscles but I knew near the finish that if I ran a fast last kilometer, I would have a good chance of breaking the record."

Just over an hour later, however, race officials announced that the time had been changed to 2:25.29. Race press officer Alan Pascoe said, "We all believed she had broken the record."

But race officials said the timekeepers had omitted rounding off Waitz's time to the nearest second when giving the initial result.

Winner of the men's race today was Britain's Mike Gratton at 2 hours 9 minutes 43 seconds. Second, also from Britain, was Gerry Helme at 2:10.12. The best male runners were missing today, drawn off by last weekend's race in Holland and Monday's Boston Marathon.

Boasting more than 18,000 contestants, London's marathon is now the biggest in the world. The course is considered the fastest among major marathons because it is relatively flat and the British spring weather tends to be cool. With temperatures in the low 50s and intermittent rain, today's race was no exception. The first 30 runners finished inside 2:15.

Waitz, 29, dominated the women's field from the outset. Her nearest challenger was Mary O'Connor at 2:28.19. Waitz cruised without any evidence of strain across the finish line on Westminster Bridge just a few hundred yards before Britain's Houses of Parliament.

Today's event was a resounding success for the competitors and the crowds rivaling those in New York and Boston that had lined London's streets. As the last finishers straggled beneath the time clock at well over five hours, knots of well-wishers were still on hand to give each runner a welcome cheer. The oldest runner, 82-year-old Alex Monro, finished in 5:24.26.

However, this year's marathon ran into some serious organizational problems that threatened its future. Gillette, which put up about $150,000 as the principal commercial sponsor of the race, announced that it would not do so next year because publicity for the company did not meet expectations.

Moreover, the race's director, former Olympic runner Christopher Brasher, clashed with its municipal backers, the Greater London Council, over permission for wheelchair contestants to take part. There was also a dispute over payment of "participation money" to leading runners--a total of $67,500--which is now legal but nonetheless remains controversial.

Despite all these problems, the marathon has become so much a fixture of London life that it seems inconceivable that it would be canceled.

About 55,000 people submitted applications to take part. Most of the 18,000 numbers were awarded on a first-come, first-served basis that produced long lines at the country's post offices last November, on the date entries were due.