WASHINGTON – The Senate on Wednesday approved a plan co-written by Sen. Susan Collins of Maine to speed generic drugs to the market and allow importers to buy U.S.-made drugs in Canada and resell them here.

Her senior colleague, Sen. Olympia Snowe, joined with Collins in favor of the legislation.

But the 78-21 vote was overshadowed by the Senate’s failed attempts earlier in the day to craft a Medicare prescription drug benefit – at least before Congress started its August recess.

The generic drug language was part of a measure by Collins and Sen. John Edwards, D-N.C., that aims to close loopholes in federal law that govern patents on prescription drugs. Under current law, pharmaceutical companies can keep on extending 30-month extensions on patents that keep generic drugs off store shelves.

The measure approved Wednesday would allow just one 30-month extension, unless a judge ordered it to continue.

But the Senate failed to agree on wording to allow a prescription drug benefit for Medicare, the vast federal health insurance program for the elderly. And Maine’s two Republican senators split on one of the proposed compromises.

The rejection virtually assures another stalemate on the issue despite its potency with voters in an election year.

Collins this week threw her support behind a Medicare prescription drug proposal known as Graham-Smith that was favored by most Senate Democrats.

Graham-Smith as well as two other proposals needed at least 60 votes to pass because of Senate budget rules.

Both Collins and Snowe had favored a so-called “tripartisan” proposal that failed last week on a 51-48 vote.

Then, after a weekend of negotiations, Collins decided to back a new compromise, called Graham-Smith after its sponsors, Sen. Bob Graham, D-Fla., and Sen. Gordon Smith, R-Ore. She said it offered an alternative that stood the best chance of passage before the August recess.

Snowe refused to support Graham-Smith, saying 70 percent of seniors would not be covered by it because their incomes were too high.

The issue is especially significant for Collins. Her Democratic challenger this year, former state Senate Majority Leader Chellie Pingree, D-North Haven, has made the prescription drug issue the centerpiece of her campaign against Collins, who is seeking a second term.

Both the “tripartisan” plan and Graham-Smith shared the same goal: providing seniors with affordable prescription drugs under Medicare. But the cost would be high: up to $400 billion over 10 years.

The difference between the proposals was how the benefit would be provided. The Graham-Smith proposal favored by Collins would have required the federal government to administer the program, while the “tripartisan” plan would have relied on private insurers.

Under the Graham-Smith compromise, low-income seniors with annual incomes of $17,720 or couples with an income of $23,880 would have been provided full drug coverage after paying a nominal monthly charge of $2 for generic drugs and $5 for brand-name drugs.

Seniors with higher incomes would have received a 5 percent discount on each prescription drug they used. If they spent more than $3,300 a year on drugs, they would have been able to pay a $10 copayment on each prescription drug and the government would have paid the remainder.

There would have been a $25 annual enrollment fee for the Graham-Smith plan, and the program would have been administered by Medicare.

Last week, Democrats backed a 10-year, $594 billion plan that would have offered benefits to all seniors enrolled in Medicare, but the measure fell short of the required 60 votes on a vote of 52-47.

After the Graham-Smith vote Wednesday, Snowe called for resumption of negotiations on a comprehensive prescription drug plan this year.

In all, the Senate has turned down four plans during the past week, including two backed mostly by Republicans as well as two drafted by Democrats.

Failure to reach agreement after five years of effort underscored the deep philosophic as well as political differences between the two parties on the issue and the difficulty of trying to create an expensive new benefit program at a time when budget surpluses have disappeared and deficits have come roaring back on Capitol Hill.