The Alexandria City Council last night tentatively approved the purchase of the Old Dominion Boat Club and the Potomac waterfront land it occupies at the foot of King Street in order to create a public park there.

The 105-year-old boat club plans to move eight blocks north along the waterfront to a city-provided site and will be paid $1.5 million if the council votes its final approval of the land deal on April 9.

Reaction to the proposed sale was mixed last night as civic groups differed on whether the benefits are worth the cost.

"It might be nice if we the city had that kind of money," said Andrea Dimond, president of the Old Town Civic Association. "But we don't and this is too expensive."

Including the assessed value of the new site for the club at the foot of Montgomery Street, the proposed sale would cost the city an estimated $4 million, council member Robert L. Calhoun said.

Ben Brenman, president of Alexandria Archaeological Commission, said he believes the Old Dominion purchase is vital to the city's multimillion-dollar waterfront development plan. "This opens the most central and critical part of the waterfront to the public: I certainly recommend we buy it."

Council member Donald C. Casey said he fully approves of the land swap and called it "a great deal for us." The King Street site "is probably worth a million more than we are paying for it."

Even if the council agrees to the sale, the transaction is contingent on the federal government approving Old Dominion's plan to rebuild its clubhouse on the new site at the foot of Montgomery street.

Because the Justice Department claims that the U.S. government owns the 1 1/2-mile strip along Alexandria's Potomac waterfront, it has successfully blocked most development plans there since 1973.

"Both we and the federal government are out for the same purpose," Mayor Charles E. Beatley said. "If the city acquires the King Street property, we should have no problem with the clouded title. We both want the land used by the public."

The council's 6-to-1 vote, with Margaret Inman in the minority, approved the sale "in concept," Beatley said, but deferred final action until details are worked out.

If the federal government refuses to allow the boathouse to rebuild on the Montgomery Street site after the council votes to purchase the property, the city still plans to purchase a 15-foot-wide strip of land along the waterfront on the King Street property. The cost for that land, where the city plans to build a promenade, was set at $75,000.

In other business, Acting City Manager Vola Lawson announced that Alexandria was named one of the eight 1984-85 All-America Cities by the National Municipal League.