Almost exactly two years after its last defeat in the state legislature, a proposal to impose a one per cent tax on the sale of higher-cost homes to pay for affordable housing on the Vineyard is again set to go before the House.

Two separate bills — one relating to the Vineyard and the other to Nantucket — were approved by the Senate last Tuesday night, giving renewed hope to affordable housing advocates.

In the case of the Vineyard, the one per cent levy would be payable by those who sold homes for more than $750,000. On Nantucket, the threshold is $2 million. Up to those thresholds, sellers would pay nothing; after that it would be $1,000 for every extra $100,000 of the price.

It is estimated the measure would raise some $2 to $3 million a year on the Vineyard, or about half the annual amount affordable housing advocates believe they need.

However, the proposal still faces a major obstacle in the House.

Two years ago, essentially the same bill passed the Senate comfortably, then got caught in traffic in the House, and was defeated just four days before the end of the session on July 31.

So far, the course of events has an air of deja vu. The proposal went to a vote in the Senate last Tuesday night and went through by a sizeable margin — 23-10.

But it is once again stuck in traffic. State Sen. Robert O’Leary, one of the bills’ sponsors, said yesterday he saw about a three-week window of opportunity to get the measure through.

“It all has to happen by the end of July or it doesn’t happen. The legislative session finishes at the end of July and then we go out of business,” he said, adding:

“There’s enough of a window, but it’s got to move fairly quickly. There’s a lot of other things out there competing for people’s attention. Realistically, we have about three weeks.

“It gets down to procedural delays. In the last two days of the session a lot of those procedural abilities to block a bill disappear, but nonetheless I’m concerned. The Senate minority leader slowed this down on the Senate side for six weeks or so.”

Nor was the situation helped by the currently stalled of negotiations over the state budget, which are holding up not only the affordable housing bill but also many other pieces of proposed legislation.

Senator O’Leary said he remained cautiously hopeful.

“I’m told by some of my colleagues on the House side that they’re a little more optimistic this time than last time,” he said.

Abbe Burt, of the Martha’s Vineyard community housing bank coalition, which has pushed the bill, said the consequences of failure this time would be more serious than two years ago.

That is because the measure is a home rule request. It was approved by meetings of all the Island towns in the spring of 2005.

After its last defeat, it was possible to submit the same bill again without going back to the towns for a fresh mandate. But if it goes down this time, she said, it would be necessary to begin the process at the town level again.

Even if the proposal does get the agreement of the House, it will still have to be approved by all the Island towns before it can go into effect.

Island Affordable Housing Trust executive director Patrick Manning said he hoped one amendment made since the bill was last defeated will make a difference this time.

“It now contains a six-year sunset clause,” he said, “Meaning it would expire in six years.

“We agreed to that because we feel so strongly that after six years people will be convinced this was the right thing to do.”

Mr. Manning said he believes that if the House passes the bill, Gov. Deval Patrick will sign it.

He called the legislation vital.

“You have such high prices, averaging in the high six hundred thousands, and yet Dukes County remains the second lowest in the state in household income. With those two factors working against you, you have to work to subsidize the housing that you are building or renovating, to provide for people,” he said, adding:

“The bottom line is, the numbers we have been working with show the need for about 250 units of affordable ownership housing and about 250 units of affordable rental housing to keep the foundation of the Island stable.”

You cannot, as he puts it, “rely on bake sales” to raise that kind of money.

Affordable housing advocates decided on a two-pronged strategy for securing a more reliable funding stream.

The first part was to push for the passage of the Community Preservation Act, so affordable housing might get funding through the towns. Affordable housing has won significant funds through CPA grants, although not as much as hoped for, over the past two years.

The second is the tax on more expensive homes.

For the past two years, Mr. Manning said, proponents had lobbied legislators heavily.

But other lobbyists have been working hard too, principally those representing real estate agents.

They argue that the measure, which would primarily affect wealthy owners of second homes, in inequitable.

“The last time this played out in the House, there was quite an extended debate on the House side,” said Senator O’Leary.

“The real estate lobby put up a real battle.”

Rep. Eric T. Turkington, another sponsor of the bills, said he remained uncertain whether enough numbers had moved in the House to get them through.

But he thought the national housing situation, now so much worse than it was two years ago, might move legislators to consider it more favorably this time.