WASHINGTON – Interest groups have burst back into action in hopes of bolstering or defeating a new Democratic push on health-care reform legislation, sparking another wave of rallies, lobbying efforts and costly advertising campaigns.

The fresh round offers a clear signal that the industries and advocacy groups most likely to be affected view the coming weeks as the final battle in determining whether Democratic proposals become law.

Their efforts suggest a return to the frenzied pace of last year’s health-care debate, which prompted more than $200 million in advocacy ads and broke records for lobbying. Companies and trade groups last year hired more than 4,500 lobbyists to influence health reform — amounting to about eight lobbyists for each member of Congress, according to an analysis by the Center for Public Integrity.

Reacting to President Obama’s recent statements that he will move ahead with legislation, health insurance companies have enlisted hundreds of lobbyists in a full-court press against the proposed overhaul. At the same time, insurers are pushing back against a bill passed by the House that would remove the industry’s antitrust exemption.

Pharmaceutical lobbyists are also targeting Obama’s plan, which includes proposals to secure an extra $10 billion in cuts from the industry and to ban deals between brand-name and generic drugmakers that keep cheaper drugs off the market.

The ramped-up effort is particularly evident among conservative groups, many of which had optimistically halted spending after Democratic reform plans were cast into doubt by the January loss of a Senate seat in Massachusetts. The 60 Plus Association announced a $500,000 television advertising campaign last week aimed at 18 centrist House Democrats, all of whom voted in favor of reform legislation last fall but whose support is now seen as wobbly.

The National Right to Life Committee has launched its own grass-roots campaign to pressure dozens of anti-abortion Democrats in the House. Americans for Prosperity also says it bought $250,000 worth of television ads last week and is laying plans for more ads and rallies.

Democratic and liberal activist groups, meanwhile, are rallying with their own efforts.

MoveOn.org, for example, said that a ”virtual march” organized Tuesday bombarded lawmakers with more than 1 million pro-reform e-mails.

One glaring exception is AARP, which has spent millions over the past year in favor of Obama’s health-care plans. A. Barry Rand, the group’s chief executive, said, ”We promise to make no new statements, send no new letters, run no new ads about health reform, and we are urging all other interest groups to do the same. Let’s turn down the volume on the outside noise so that our leaders might actually listen.”