The Northern Virginia Regional Park Authority Tuesday night approved creation of a major urban park in Alexandria's Cameron Run Valley.

But the approval was conditioned on future determination of what kind of part will be created on the 40-to-50-acre site on the city's southern border, along the Capital Beltway west of Telegraph Road.

The city has proposed building a road Eisenhower Avenue - through the park, and the park authority asked the city to take no further action on the road and to study alternatives to it.

The issue split the park agency's six-member jurisdictions, with Fairfax County and Fairfax City members voting against the Alexandria park site. Arlington, Falls Church Loudoun County and Alexandria members voted for it.

The vote commits the authority to a major study of possibly uses for the park, expected to cost at least $50,000.

The park authority could spend up to $1 million developing the park, money included for a major urban park in its five-year capital improvement program.

Fairfax City member Leonard A. Mobley accused Alexandria of "pushing us . . . blackmailing us into this" and charged that the park authority was reversing its policy of preserving large segments of parkland in rural areas. Park authority board chairman Walter L. Mess, who voted for the park, said, "I believe the park should be where the people are.